SDL2来源分析3：渲染（SDL_Renderer）
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SDL2来源分析3：渲染（SDL_Renderer）
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SDL源代碼分析系列文章上市：
SDL2源碼分析1：初始化（SDL_Init()）
SDL2源碼分析2：窗體（SDL_Window）
SDL2源碼分析3：渲染器（SDL_Renderer）
SDL2源碼分析4：紋理（SDL_Texture）
SDL2源碼分析5：更新紋理（SDL_UpdateTexture()）
SDL2源碼分析6：拷貝到渲染器（SDL_RenderCopy()）
SDL2源碼分析7：顯示（SDL_RenderPresent()）
SDL2源碼分析8：視頻顯示總結
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上一篇文章分析了SDL中創建窗體的函數SDL_CreateWindow()。這篇文章繼續分析SDL的源碼。
本文分析SDL的渲染器（SDL_Renderer）。
SDL播放視頻的代碼流程例如以下所看到的。
初始化:
SDL_Init(): 初始化SDL。
SDL_CreateWindow(): 創建窗體（Window）。
SDL_CreateRenderer(): 基于窗體創建渲染器（Render）。
SDL_CreateTexture(): 創建紋理（Texture）。
循環渲染數據:
SDL_UpdateTexture(): 設置紋理的數據。
SDL_RenderCopy(): 紋理復制給渲染器。SDL_RenderPresent(): 顯示。
上篇文章分析了該流程中的第2個函數SDL_CreateWindow()。
本文繼續分析該流程中的第3個函數SDL_CreateRenderer()。
SDL_Renderer
SDL_Renderer結構體定義了一個SDL2中的渲染器。假設直接使用SDL2編譯好的SDK的話。是看不到它的內部結構的。
有關它的定義在頭文件里僅僅有一行代碼。例如以下所看到的。
/** * rief A structure representing rendering state */ struct SDL_Renderer; typedef struct SDL_Renderer SDL_Renderer;
在源碼project中能夠看到SDL_Renderer的定義，位于renderSDL_sysrender.h文件里。
它的定義例如以下。
/* Define the SDL renderer structure */
struct SDL_Renderer
{
const void *magic;
void (*WindowEvent) (SDL_Renderer * renderer, const SDL_WindowEvent *event);
int (*GetOutputSize) (SDL_Renderer * renderer, int *w, int *h);
int (*CreateTexture) (SDL_Renderer * renderer, SDL_Texture * texture);
int (*SetTextureColorMod) (SDL_Renderer * renderer,
SDL_Texture * texture);
int (*SetTextureAlphaMod) (SDL_Renderer * renderer,
SDL_Texture * texture);
int (*SetTextureBlendMode) (SDL_Renderer * renderer,
SDL_Texture * texture);
int (*UpdateTexture) (SDL_Renderer * renderer, SDL_Texture * texture,
const SDL_Rect * rect, const void *pixels,
int pitch);
int (*UpdateTextureYUV) (SDL_Renderer * renderer, SDL_Texture * texture,
const SDL_Rect * rect,
const Uint8 *Yplane, int Ypitch,
const Uint8 *Uplane, int Upitch,
const Uint8 *Vplane, int Vpitch);
int (*LockTexture) (SDL_Renderer * renderer, SDL_Texture * texture,
const SDL_Rect * rect, void **pixels, int *pitch);
void (*UnlockTexture) (SDL_Renderer * renderer, SDL_Texture * texture);
int (*SetRenderTarget) (SDL_Renderer * renderer, SDL_Texture * texture);
int (*UpdateViewport) (SDL_Renderer * renderer);
int (*UpdateClipRect) (SDL_Renderer * renderer);
int (*RenderClear) (SDL_Renderer * renderer);
int (*RenderDrawPoints) (SDL_Renderer * renderer, const SDL_FPoint * points,
int count);
int (*RenderDrawLines) (SDL_Renderer * renderer, const SDL_FPoint * points,
int count);
int (*RenderFillRects) (SDL_Renderer * renderer, const SDL_FRect * rects,
int count);
int (*RenderCopy) (SDL_Renderer * renderer, SDL_Texture * texture,
const SDL_Rect * srcrect, const SDL_FRect * dstrect);
int (*RenderCopyEx) (SDL_Renderer * renderer, SDL_Texture * texture,
const SDL_Rect * srcquad, const SDL_FRect * dstrect,
const double angle, const SDL_FPoint *center, const SDL_RendererFlip flip);
int (*RenderReadPixels) (SDL_Renderer * renderer, const SDL_Rect * rect,
Uint32 format, void * pixels, int pitch);
void (*RenderPresent) (SDL_Renderer * renderer);
void (*DestroyTexture) (SDL_Renderer * renderer, SDL_Texture * texture);
void (*DestroyRenderer) (SDL_Renderer * renderer);
int (*GL_BindTexture) (SDL_Renderer * renderer, SDL_Texture *texture, float *texw, float *texh);
int (*GL_UnbindTexture) (SDL_Renderer * renderer, SDL_Texture *texture);
/* The current renderer info */
SDL_RendererInfo info;
/* The window associated with the renderer */
SDL_Window *window;
SDL_bool hidden;
/* The logical resolution for rendering */
int logical_w;
int logical_h;
int logical_w_backup;
int logical_h_backup;
/* The drawable area within the window */
SDL_Rect viewport;
SDL_Rect viewport_backup;
/* The clip rectangle within the window */
SDL_Rect clip_rect;
SDL_Rect clip_rect_backup;
/* The render output coordinate scale */
SDL_FPoint scale;
SDL_FPoint scale_backup;
/* The list of textures */
SDL_Texture *textures;
SDL_Texture *target;
Uint8 r, g, b, a; /**< Color for drawing operations values */
SDL_BlendMode blendMode; /**< The drawing blend mode */
void *driverdata;
};
通過代碼能夠看出當中包括了一個“渲染器”應該包括的各種屬性。
這個結構體中的各個變量還沒有深入研究，暫不具體分析。
以下來看看怎樣創建這個SDL_Renderer。
SDL_CreateRenderer()
函數簡單介紹
SDL中使用SDL_CreateRenderer()基于窗體創建渲染器。SDL_CreateRenderer()原型例如以下。
SDL_Renderer * SDLCALL SDL_CreateRenderer(SDL_Window * window,
int index, Uint32 flags);
參數含義例如以下。
window ： 渲染的目標窗體。
index ：打算初始化的渲染設備的索引。
設置“-1”則初始化默認的渲染設備。
flags ：支持以下值（位于SDL_RendererFlags定義中）
SDL_RENDERER_SOFTWARE ：使用軟件渲染
SDL_RENDERER_ACCELERATED ：使用硬件加速
SDL_RENDERER_PRESENTVSYNC：和顯示器的刷新率同步
SDL_RENDERER_TARGETTEXTURE ：不太懂
返回創建完畢的渲染器的ID。假設創建失敗則返回NULL。
函數調用關系圖
SDL_CreateRenderer()關鍵函數的調用關系能夠用下圖表示。
上述圖片不太清晰，相冊里面上傳了一份原始的大圖片：
http://my.csdn.net/leixiaohua1020/album/detail/1793385
打開上述相冊里面的圖片，右鍵選擇“另存為”就可以保存原始圖片。
源碼分析
SDL_CreateRenderer()的源碼位于renderSDL_render.c中，例如以下所看到的。
SDL_Renderer * SDL_CreateRenderer(SDL_Window * window, int index, Uint32 flags)
{
#if !SDL_RENDER_DISABLED
SDL_Renderer *renderer = NULL;
int n = SDL_GetNumRenderDrivers();
const char *hint;
if (!window) {
SDL_SetError("Invalid window");
return NULL;
}
if (SDL_GetRenderer(window)) {
SDL_SetError("Renderer already associated with window");
return NULL;
}
hint = SDL_GetHint(SDL_HINT_RENDER_VSYNC);
if (hint) {
if (*hint == '0') {
flags &= ~SDL_RENDERER_PRESENTVSYNC;
} else {
flags |= SDL_RENDERER_PRESENTVSYNC;
}
}
if (index < 0) {
hint = SDL_GetHint(SDL_HINT_RENDER_DRIVER);
if (hint) {
for (index = 0; index < n; ++index) {
const SDL_RenderDriver *driver = render_drivers[index];
if (SDL_strcasecmp(hint, driver->info.name) == 0) {
/* Create a new renderer instance */
renderer = driver->CreateRenderer(window, flags);
break;
}
}
}
if (!renderer) {
for (index = 0; index < n; ++index) {
const SDL_RenderDriver *driver = render_drivers[index];
if ((driver->info.flags & flags) == flags) {
/* Create a new renderer instance */
renderer = driver->CreateRenderer(window, flags);
if (renderer) {
/* Yay, we got one! */
break;
}
}
}
}
if (index == n) {
SDL_SetError("Couldn't find matching render driver");
return NULL;
}
} else {
if (index >= SDL_GetNumRenderDrivers()) {
SDL_SetError("index must be -1 or in the range of 0 - %d",
SDL_GetNumRenderDrivers() - 1);
return NULL;
}
/* Create a new renderer instance */
renderer = render_drivers[index]->CreateRenderer(window, flags);
}
if (renderer) {
renderer->magic = &renderer_magic;
renderer->window = window;
renderer->scale.x = 1.0f;
renderer->scale.y = 1.0f;
if (SDL_GetWindowFlags(window) & (SDL_WINDOW_HIDDEN|SDL_WINDOW_MINIMIZED)) {
renderer->hidden = SDL_TRUE;
} else {
renderer->hidden = SDL_FALSE;
}
SDL_SetWindowData(window, SDL_WINDOWRENDERDATA, renderer);
SDL_RenderSetViewport(renderer, NULL);
SDL_AddEventWatch(SDL_RendererEventWatch, renderer);
SDL_LogInfo(SDL_LOG_CATEGORY_RENDER,
"Created renderer: %s", renderer->info.name);
}
return renderer;
#else
SDL_SetError("SDL not built with rendering support");
return NULL;
#endif
}
SDL_CreateRenderer()中最重要的一個函數就是它調用了SDL_RenderDriver的CreateRenderer()方法。通過該方法能夠創建一個渲染器。
環繞著這種方法，包括了一些初始化工作以及一些收尾工作。
以下針對這個最核心的函數進行分析。
我們首先來看一下SDL_RenderDriver這個結構體。從字面的意思能夠看出它代表了“渲染器的驅動程序”。
這個結構體的定義例如以下。
/* Define the SDL render driver structure */
struct SDL_RenderDriver
{
SDL_Renderer *(*CreateRenderer) (SDL_Window * window, Uint32 flags);
/* Info about the renderer capabilities */
SDL_RendererInfo info;
};
從代碼中能夠看出，這個結構體的成員比較簡單。包括了一個函數指針CreateRenderer()和一個存儲信息的SDL_RendererInfo類型的結構體info。CreateRenderer()是用于創建渲染器的函數，而SDL_RendererInfo則包括了該結構體的一些信息。能夠看一下SDL_RendererInfo的定義。
/**
* rief Information on the capabilities of a render driver or context.
*/
typedef struct SDL_RendererInfo
{
const char *name; /**< The name of the renderer */
Uint32 flags; /**< Supported ::SDL_RendererFlags */
Uint32 num_texture_formats; /**< The number of available texture formats */
Uint32 texture_formats[16]; /**< The available texture formats */
int max_texture_width; /**< The maximimum texture width */
int max_texture_height; /**< The maximimum texture height */
} SDL_RendererInfo;
在SDL中有一個全局的SDL_RenderDriver類型的靜態數組render_drivers，當中存儲了SDL支持的全部渲染器。
該數組定義例如以下。
static const SDL_RenderDriver *render_drivers[] = {
#if SDL_VIDEO_RENDER_D3D
&D3D_RenderDriver,
#endif
#if SDL_VIDEO_RENDER_D3D11
&D3D11_RenderDriver,
#endif
#if SDL_VIDEO_RENDER_OGL
&GL_RenderDriver,
#endif
#if SDL_VIDEO_RENDER_OGL_ES2
&GLES2_RenderDriver,
#endif
#if SDL_VIDEO_RENDER_OGL_ES
&GLES_RenderDriver,
#endif
#if SDL_VIDEO_RENDER_DIRECTFB
&DirectFB_RenderDriver,
#endif
#if SDL_VIDEO_RENDER_PSP
&PSP_RenderDriver,
#endif
&SW_RenderDriver
};
從render_drivers數組的定義能夠看出，當中包括了Direct3D，OpenGL。OpenGL ES等各種渲染器的驅動程序。
我們能夠選擇幾個看一下。
比如Direct3D的渲染器驅動程序D3D_RenderDriver的定義例如以下（位于renderdirect3dSDL_render_d3d.c）。
SDL_RenderDriver D3D_RenderDriver = {
D3D_CreateRenderer,
{
"direct3d",
(SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC | SDL_RENDERER_TARGETTEXTURE),
1,
{SDL_PIXELFORMAT_ARGB8888},
0,
0}
};
能夠看出創建Direct3D渲染器的函數是D3D_CreateRenderer()。
OpenGL的渲染器驅動程序GL_RenderDriver的定義例如以下（位于renderopenglSDL_render_gl.c）。
SDL_RenderDriver GL_RenderDriver = {
GL_CreateRenderer,
{
"opengl",
(SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC | SDL_RENDERER_TARGETTEXTURE),
1,
{SDL_PIXELFORMAT_ARGB8888},
0,
0}
};
能夠看出創建OpenGL渲染器的函數是GL_CreateRenderer()。
軟件渲染器驅動程序SW_RenderDriver的定義例如以下（位于rendersoftwareSDL_render_sw.c）。
SDL_RenderDriver SW_RenderDriver = {
SW_CreateRenderer,
{
"software",
SDL_RENDERER_SOFTWARE | SDL_RENDERER_TARGETTEXTURE,
8,
{
SDL_PIXELFORMAT_RGB555,
SDL_PIXELFORMAT_RGB565,
SDL_PIXELFORMAT_RGB888,
SDL_PIXELFORMAT_BGR888,
SDL_PIXELFORMAT_ARGB8888,
SDL_PIXELFORMAT_RGBA8888,
SDL_PIXELFORMAT_ABGR8888,
SDL_PIXELFORMAT_BGRA8888
},
0,
0}
};
能夠看出創建軟件渲染器的函數是SW_CreateRenderer ()。
有關SDL_RenderDriver這個結構體就不再多說了。以下分別看一下Direct3D，OpenGL，Software這三種最常見的渲染器的創建方法。
1. Direct3D
Direct3D 的渲染器在創建函數是D3D_CreateRenderer()。該函數位于renderdirect3dSDL_render_d3d.c文件里。首先看一下它的代碼。
SDL_Renderer * D3D_CreateRenderer(SDL_Window * window, Uint32 flags)
{
SDL_Renderer *renderer;
D3D_RenderData *data;
SDL_SysWMinfo windowinfo;
HRESULT result;
const char *hint;
D3DPRESENT_PARAMETERS pparams;
IDirect3DSwapChain9 *chain;
D3DCAPS9 caps;
DWORD device_flags;
Uint32 window_flags;
int w, h;
SDL_DisplayMode fullscreen_mode;
int displayIndex;
renderer = (SDL_Renderer *) SDL_calloc(1, sizeof(*renderer));
if (!renderer) {
SDL_OutOfMemory();
return NULL;
}
data = (D3D_RenderData *) SDL_calloc(1, sizeof(*data));
if (!data) {
SDL_free(renderer);
SDL_OutOfMemory();
return NULL;
}
if (!D3D_LoadDLL(&data->d3dDLL, &data->d3d)) {
SDL_free(renderer);
SDL_free(data);
SDL_SetError("Unable to create Direct3D interface");
return NULL;
}
renderer->WindowEvent = D3D_WindowEvent;
renderer->CreateTexture = D3D_CreateTexture;
renderer->UpdateTexture = D3D_UpdateTexture;
renderer->UpdateTextureYUV = D3D_UpdateTextureYUV;
renderer->LockTexture = D3D_LockTexture;
renderer->UnlockTexture = D3D_UnlockTexture;
renderer->SetRenderTarget = D3D_SetRenderTarget;
renderer->UpdateViewport = D3D_UpdateViewport;
renderer->UpdateClipRect = D3D_UpdateClipRect;
renderer->RenderClear = D3D_RenderClear;
renderer->RenderDrawPoints = D3D_RenderDrawPoints;
renderer->RenderDrawLines = D3D_RenderDrawLines;
renderer->RenderFillRects = D3D_RenderFillRects;
renderer->RenderCopy = D3D_RenderCopy;
renderer->RenderCopyEx = D3D_RenderCopyEx;
renderer->RenderReadPixels = D3D_RenderReadPixels;
renderer->RenderPresent = D3D_RenderPresent;
renderer->DestroyTexture = D3D_DestroyTexture;
renderer->DestroyRenderer = D3D_DestroyRenderer;
renderer->info = D3D_RenderDriver.info;
renderer->info.flags = (SDL_RENDERER_ACCELERATED | SDL_RENDERER_TARGETTEXTURE);
renderer->driverdata = data;
SDL_VERSION(&windowinfo.version);
SDL_GetWindowWMInfo(window, &windowinfo);
window_flags = SDL_GetWindowFlags(window);
SDL_GetWindowSize(window, &w, &h);
SDL_GetWindowDisplayMode(window, &fullscreen_mode);
SDL_zero(pparams);
pparams.hDeviceWindow = windowinfo.info.win.window;
pparams.BackBufferWidth = w;
pparams.BackBufferHeight = h;
if (window_flags & SDL_WINDOW_FULLSCREEN) {
pparams.BackBufferFormat =
PixelFormatToD3DFMT(fullscreen_mode.format);
} else {
pparams.BackBufferFormat = D3DFMT_UNKNOWN;
}
pparams.BackBufferCount = 1;
pparams.SwapEffect = D3DSWAPEFFECT_DISCARD;
if (window_flags & SDL_WINDOW_FULLSCREEN) {
if ((window_flags & SDL_WINDOW_FULLSCREEN_DESKTOP) == SDL_WINDOW_FULLSCREEN_DESKTOP) {
pparams.Windowed = TRUE;
pparams.FullScreen_RefreshRateInHz = 0;
} else {
pparams.Windowed = FALSE;
pparams.FullScreen_RefreshRateInHz = fullscreen_mode.refresh_rate;
}
} else {
pparams.Windowed = TRUE;
pparams.FullScreen_RefreshRateInHz = 0;
}
if (flags & SDL_RENDERER_PRESENTVSYNC) {
pparams.PresentationInterval = D3DPRESENT_INTERVAL_ONE;
} else {
pparams.PresentationInterval = D3DPRESENT_INTERVAL_IMMEDIATE;
}
/* Get the adapter for the display that the window is on */
displayIndex = SDL_GetWindowDisplayIndex(window);
data->adapter = SDL_Direct3D9GetAdapterIndex(displayIndex);
IDirect3D9_GetDeviceCaps(data->d3d, data->adapter, D3DDEVTYPE_HAL, &caps);
device_flags = D3DCREATE_FPU_PRESERVE;
if (caps.DevCaps & D3DDEVCAPS_HWTRANSFORMANDLIGHT) {
device_flags |= D3DCREATE_HARDWARE_VERTEXPROCESSING;
} else {
device_flags |= D3DCREATE_SOFTWARE_VERTEXPROCESSING;
}
hint = SDL_GetHint(SDL_HINT_RENDER_DIRECT3D_THREADSAFE);
if (hint && SDL_atoi(hint)) {
device_flags |= D3DCREATE_MULTITHREADED;
}
result = IDirect3D9_CreateDevice(data->d3d, data->adapter,
D3DDEVTYPE_HAL,
pparams.hDeviceWindow,
device_flags,
&pparams, &data->device);
if (FAILED(result)) {
D3D_DestroyRenderer(renderer);
D3D_SetError("CreateDevice()", result);
return NULL;
}
/* Get presentation parameters to fill info */
result = IDirect3DDevice9_GetSwapChain(data->device, 0, &chain);
if (FAILED(result)) {
D3D_DestroyRenderer(renderer);
D3D_SetError("GetSwapChain()", result);
return NULL;
}
result = IDirect3DSwapChain9_GetPresentParameters(chain, &pparams);
if (FAILED(result)) {
IDirect3DSwapChain9_Release(chain);
D3D_DestroyRenderer(renderer);
D3D_SetError("GetPresentParameters()", result);
return NULL;
}
IDirect3DSwapChain9_Release(chain);
if (pparams.PresentationInterval == D3DPRESENT_INTERVAL_ONE) {
renderer->info.flags |= SDL_RENDERER_PRESENTVSYNC;
}
data->pparams = pparams;
IDirect3DDevice9_GetDeviceCaps(data->device, &caps);
renderer->info.max_texture_width = caps.MaxTextureWidth;
renderer->info.max_texture_height = caps.MaxTextureHeight;
if (caps.NumSimultaneousRTs >= 2) {
renderer->info.flags |= SDL_RENDERER_TARGETTEXTURE;
}
if (caps.PrimitiveMiscCaps & D3DPMISCCAPS_SEPARATEALPHABLEND) {
data->enableSeparateAlphaBlend = SDL_TRUE;
}
/* Store the default render target */
IDirect3DDevice9_GetRenderTarget(data->device, 0, &data->defaultRenderTarget );
data->currentRenderTarget = NULL;
/* Set up parameters for rendering */
D3D_InitRenderState(data);
if (caps.MaxSimultaneousTextures >= 3)
{
#ifdef ASSEMBLE_SHADER
/* This shader was created by running the following HLSL through the fxc compiler
and then tuning the generated assembly.
fxc /T fx_4_0 /O3 /Gfa /Fc yuv.fxc yuv.fx
--- yuv.fx ---
Texture2D g_txY;
Texture2D g_txU;
Texture2D g_txV;
SamplerState samLinear
{
Filter = ANISOTROPIC;
AddressU = Clamp;
AddressV = Clamp;
MaxAnisotropy = 1;
};
struct VS_OUTPUT
{
float2 TextureUV : TEXCOORD0;
};
struct PS_OUTPUT
{
float4 RGBAColor : SV_Target;
};
PS_OUTPUT YUV420( VS_OUTPUT In )
{
const float3 offset = {-0.0625, -0.5, -0.5};
const float3 Rcoeff = {1.164, 0.000, 1.596};
const float3 Gcoeff = {1.164, -0.391, -0.813};
const float3 Bcoeff = {1.164, 2.018, 0.000};
PS_OUTPUT Output;
float2 TextureUV = In.TextureUV;
float3 yuv;
yuv.x = g_txY.Sample( samLinear, TextureUV ).r;
yuv.y = g_txU.Sample( samLinear, TextureUV ).r;
yuv.z = g_txV.Sample( samLinear, TextureUV ).r;
yuv += offset;
Output.RGBAColor.r = dot(yuv, Rcoeff);
Output.RGBAColor.g = dot(yuv, Gcoeff);
Output.RGBAColor.b = dot(yuv, Bcoeff);
Output.RGBAColor.a = 1.0f;
return Output;
}
technique10 RenderYUV420
{
pass P0
{
SetPixelShader( CompileShader( ps_4_0_level_9_0, YUV420() ) );
}
}
*/
const char *shader_text =
"ps_2_0
"
"def c0, -0.0625, -0.5, -0.5, 1
"
"def c1, 1.16400003, 0, 1.59599996, 0
"
"def c2, 1.16400003, -0.391000003, -0.813000023, 0
"
"def c3, 1.16400003, 2.01799989, 0, 0
"
"dcl t0.xy
"
"dcl v0.xyzw
"
"dcl_2d s0
"
"dcl_2d s1
"
"dcl_2d s2
"
"texld r0, t0, s0
"
"texld r1, t0, s1
"
"texld r2, t0, s2
"
"mov r0.y, r1.x
"
"mov r0.z, r2.x
"
"add r0.xyz, r0, c0
"
"dp3 r1.x, r0, c1
"
"dp3 r1.y, r0, c2
"
"dp2add r1.z, r0, c3, c3.z
" /* Logically this is "dp3 r1.z, r0, c3" but the optimizer did its magic */
"mov r1.w, c0.w
"
"mul r0, r1, v0
" /* Not in the HLSL, multiply by vertex color */
"mov oC0, r0
"
;
LPD3DXBUFFER pCode;
LPD3DXBUFFER pErrorMsgs;
LPDWORD shader_data = NULL;
DWORD shader_size = 0;
result = D3DXAssembleShader(shader_text, SDL_strlen(shader_text), NULL, NULL, 0, &pCode, &pErrorMsgs);
if (!FAILED(result)) {
shader_data = (DWORD*)pCode->lpVtbl->GetBufferPointer(pCode);
shader_size = pCode->lpVtbl->GetBufferSize(pCode);
PrintShaderData(shader_data, shader_size);
} else {
const char *error = (const char *)pErrorMsgs->lpVtbl->GetBufferPointer(pErrorMsgs);
SDL_SetError("Couldn't assemble shader: %s", error);
}
#else
const DWORD shader_data[] = {
0xffff0200, 0x05000051, 0xa00f0000, 0xbd800000, 0xbf000000, 0xbf000000,
0x3f800000, 0x05000051, 0xa00f0001, 0x3f94fdf4, 0x00000000, 0x3fcc49ba,
0x00000000, 0x05000051, 0xa00f0002, 0x3f94fdf4, 0xbec83127, 0xbf5020c5,
0x00000000, 0x05000051, 0xa00f0003, 0x3f94fdf4, 0x400126e9, 0x00000000,
0x00000000, 0x0200001f, 0x80000000, 0xb0030000, 0x0200001f, 0x80000000,
0x900f0000, 0x0200001f, 0x90000000, 0xa00f0800, 0x0200001f, 0x90000000,
0xa00f0801, 0x0200001f, 0x90000000, 0xa00f0802, 0x03000042, 0x800f0000,
0xb0e40000, 0xa0e40800, 0x03000042, 0x800f0001, 0xb0e40000, 0xa0e40801,
0x03000042, 0x800f0002, 0xb0e40000, 0xa0e40802, 0x02000001, 0x80020000,
0x80000001, 0x02000001, 0x80040000, 0x80000002, 0x03000002, 0x80070000,
0x80e40000, 0xa0e40000, 0x03000008, 0x80010001, 0x80e40000, 0xa0e40001,
0x03000008, 0x80020001, 0x80e40000, 0xa0e40002, 0x0400005a, 0x80040001,
0x80e40000, 0xa0e40003, 0xa0aa0003, 0x02000001, 0x80080001, 0xa0ff0000,
0x03000005, 0x800f0000, 0x80e40001, 0x90e40000, 0x02000001, 0x800f0800,
0x80e40000, 0x0000ffff
};
#endif
if (shader_data != NULL) {
result = IDirect3DDevice9_CreatePixelShader(data->device, shader_data, &data->ps_yuv);
if (!FAILED(result)) {
renderer->info.texture_formats[renderer->info.num_texture_formats++] = SDL_PIXELFORMAT_YV12;
renderer->info.texture_formats[renderer->info.num_texture_formats++] = SDL_PIXELFORMAT_IYUV;
} else {
D3D_SetError("CreatePixelShader()", result);
}
}
}
return renderer;
}
D3D_CreateRenderer()這個函數的代碼非常長。在這里提取它最重點的幾個進行簡單的分析。
PS：因為這個函數中包括了大量的Direct3D的API。這方面假設不熟悉的話。能夠參考以下兩篇文章：
《最簡單的視音頻播放演示樣例3：Direct3D播放YUV，RGB（通過Surface）》
《最簡單的視音頻播放演示樣例4：Direct3D播放RGB（通過Texture）》
（1） 為SDL_Renderer分配內存
這一步比較簡單。直接使用SDL_calloc()分配內存就能夠了。
SDL_calloc()實際上就是calloc()。這一點在前面的文章中已經敘述，在這里不再反復。
（2） 載入Direct3D
載入Direct3D通過函數D3D_LoadDLL()完畢。
調用該函數能夠得到一個IDirect3D9類型的接口。IDirect3D9接口能夠用于完畢D3D興許的初始化工作。
D3D_LoadDLL()函數的代碼例如以下。
SDL_bool D3D_LoadDLL( void **pD3DDLL, IDirect3D9 **pDirect3D9Interface )
{
*pD3DDLL = SDL_LoadObject("D3D9.DLL");
if (*pD3DDLL) {
IDirect3D9 *(WINAPI * D3DCreate) (UINT SDKVersion);
D3DCreate =
(IDirect3D9 * (WINAPI *) (UINT)) SDL_LoadFunction(*pD3DDLL,
"Direct3DCreate9");
if (D3DCreate) {
*pDirect3D9Interface = D3DCreate(D3D_SDK_VERSION);
}
if (!*pDirect3D9Interface) {
SDL_UnloadObject(*pD3DDLL);
*pD3DDLL = NULL;
return SDL_FALSE;
}
return SDL_TRUE;
} else {
*pDirect3D9Interface = NULL;
return SDL_FALSE;
}
}
從代碼中能夠看出，該函數載入了一個“D3D9.DLL”的Dll。而且調用了當中的Direct3DCreate9()方法。
（3） 渲染器接口函數賦值
SDL_Render結構體中有一系列的函數指針，包括了有關渲染器的各種功能。SDL通過調用這些函數指針就能夠調用渲染器相應的功能。這是SDL支持多種渲染器的一個重要特點。代碼例如以下所看到的。
renderer->WindowEvent = D3D_WindowEvent;
renderer->CreateTexture = D3D_CreateTexture;
renderer->UpdateTexture = D3D_UpdateTexture;
renderer->UpdateTextureYUV = D3D_UpdateTextureYUV;
renderer->LockTexture = D3D_LockTexture;
renderer->UnlockTexture = D3D_UnlockTexture;
renderer->SetRenderTarget = D3D_SetRenderTarget;
renderer->UpdateViewport = D3D_UpdateViewport;
renderer->UpdateClipRect = D3D_UpdateClipRect;
renderer->RenderClear = D3D_RenderClear;
renderer->RenderDrawPoints = D3D_RenderDrawPoints;
renderer->RenderDrawLines = D3D_RenderDrawLines;
renderer->RenderFillRects = D3D_RenderFillRects;
renderer->RenderCopy = D3D_RenderCopy;
renderer->RenderCopyEx = D3D_RenderCopyEx;
renderer->RenderReadPixels = D3D_RenderReadPixels;
renderer->RenderPresent = D3D_RenderPresent;
renderer->DestroyTexture = D3D_DestroyTexture;
renderer->DestroyRenderer = D3D_DestroyRenderer;
（4） 創建Device
創建Direct3D的Device通過IDirect3D9_CreateDevice()函數來實現。這一方面的知識不再敘述，能夠參考Direct3D創建Device的相關的文章。
（5） 設置渲染狀態
設置渲染狀態在函數D3D_InitRenderState()中完畢。該部分的知識也不再詳述，能夠參考Direct3D相關的渲染教程。貼出D3D_InitRenderState()的代碼。
static void D3D_InitRenderState(D3D_RenderData *data)
{
D3DMATRIX matrix;
IDirect3DDevice9 *device = data->device;
IDirect3DDevice9_SetVertexShader(device, NULL);
IDirect3DDevice9_SetFVF(device, D3DFVF_XYZ | D3DFVF_DIFFUSE | D3DFVF_TEX1);
IDirect3DDevice9_SetRenderState(device, D3DRS_ZENABLE, D3DZB_FALSE);
IDirect3DDevice9_SetRenderState(device, D3DRS_CULLMODE, D3DCULL_NONE);
IDirect3DDevice9_SetRenderState(device, D3DRS_LIGHTING, FALSE);
/* Enable color modulation by diffuse color */
IDirect3DDevice9_SetTextureStageState(device, 0, D3DTSS_COLOROP,
D3DTOP_MODULATE);
IDirect3DDevice9_SetTextureStageState(device, 0, D3DTSS_COLORARG1,
D3DTA_TEXTURE);
IDirect3DDevice9_SetTextureStageState(device, 0, D3DTSS_COLORARG2,
D3DTA_DIFFUSE);
/* Enable alpha modulation by diffuse alpha */
IDirect3DDevice9_SetTextureStageState(device, 0, D3DTSS_ALPHAOP,
D3DTOP_MODULATE);
IDirect3DDevice9_SetTextureStageState(device, 0, D3DTSS_ALPHAARG1,
D3DTA_TEXTURE);
IDirect3DDevice9_SetTextureStageState(device, 0, D3DTSS_ALPHAARG2,
D3DTA_DIFFUSE);
/* Enable separate alpha blend function, if possible */
if (data->enableSeparateAlphaBlend) {
IDirect3DDevice9_SetRenderState(device, D3DRS_SEPARATEALPHABLENDENABLE, TRUE);
}
/* Disable second texture stage, since we're done */
IDirect3DDevice9_SetTextureStageState(device, 1, D3DTSS_COLOROP,
D3DTOP_DISABLE);
IDirect3DDevice9_SetTextureStageState(device, 1, D3DTSS_ALPHAOP,
D3DTOP_DISABLE);
/* Set an identity world and view matrix */
matrix.m[0][0] = 1.0f;
matrix.m[0][1] = 0.0f;
matrix.m[0][2] = 0.0f;
matrix.m[0][3] = 0.0f;
matrix.m[1][0] = 0.0f;
matrix.m[1][1] = 1.0f;
matrix.m[1][2] = 0.0f;
matrix.m[1][3] = 0.0f;
matrix.m[2][0] = 0.0f;
matrix.m[2][1] = 0.0f;
matrix.m[2][2] = 1.0f;
matrix.m[2][3] = 0.0f;
matrix.m[3][0] = 0.0f;
matrix.m[3][1] = 0.0f;
matrix.m[3][2] = 0.0f;
matrix.m[3][3] = 1.0f;
IDirect3DDevice9_SetTransform(device, D3DTS_WORLD, &matrix);
IDirect3DDevice9_SetTransform(device, D3DTS_VIEW, &matrix);
/* Reset our current scale mode */
SDL_memset(data->scaleMode, 0xFF, sizeof(data->scaleMode));
/* Start the render with beginScene */
data->beginScene = SDL_TRUE;
}
（6） 創建Shader
創建Shader通過函數IDirect3DDevice9_CreatePixelShader()完畢。
完畢以上步驟之后，Direct3D的渲染器就創建完畢了。
2. OpenGL
OpenGL 的渲染器在創建函數是GL_CreateRenderer()。該函數位于renderopenglSDL_render_gl.c文件里。首先看一下它的代碼。
PS：當中用到了OpenGL的非常多API。假設對OpenGL的API還不熟悉的話，能夠參考文章：
《最簡單的視音頻播放演示樣例6：OpenGL播放YUV420P（通過Texture，使用Shader）》
SDL_Renderer * GL_CreateRenderer(SDL_Window * window, Uint32 flags)
{
SDL_Renderer *renderer;
GL_RenderData *data;
const char *hint;
GLint value;
Uint32 window_flags;
int profile_mask, major, minor;
SDL_GL_GetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, &profile_mask);
SDL_GL_GetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, &major);
SDL_GL_GetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, &minor);
window_flags = SDL_GetWindowFlags(window);
if (!(window_flags & SDL_WINDOW_OPENGL) ||
profile_mask == SDL_GL_CONTEXT_PROFILE_ES || major != RENDERER_CONTEXT_MAJOR || minor != RENDERER_CONTEXT_MINOR) {
SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, 0);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, RENDERER_CONTEXT_MAJOR);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, RENDERER_CONTEXT_MINOR);
if (SDL_RecreateWindow(window, window_flags | SDL_WINDOW_OPENGL) < 0) {
/* Uh oh, better try to put it back... */
SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, profile_mask);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, major);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, minor);
SDL_RecreateWindow(window, window_flags);
return NULL;
}
}
renderer = (SDL_Renderer *) SDL_calloc(1, sizeof(*renderer));
if (!renderer) {
SDL_OutOfMemory();
return NULL;
}
data = (GL_RenderData *) SDL_calloc(1, sizeof(*data));
if (!data) {
GL_DestroyRenderer(renderer);
SDL_OutOfMemory();
return NULL;
}
renderer->WindowEvent = GL_WindowEvent;
renderer->GetOutputSize = GL_GetOutputSize;
renderer->CreateTexture = GL_CreateTexture;
renderer->UpdateTexture = GL_UpdateTexture;
renderer->UpdateTextureYUV = GL_UpdateTextureYUV;
renderer->LockTexture = GL_LockTexture;
renderer->UnlockTexture = GL_UnlockTexture;
renderer->SetRenderTarget = GL_SetRenderTarget;
renderer->UpdateViewport = GL_UpdateViewport;
renderer->UpdateClipRect = GL_UpdateClipRect;
renderer->RenderClear = GL_RenderClear;
renderer->RenderDrawPoints = GL_RenderDrawPoints;
renderer->RenderDrawLines = GL_RenderDrawLines;
renderer->RenderFillRects = GL_RenderFillRects;
renderer->RenderCopy = GL_RenderCopy;
renderer->RenderCopyEx = GL_RenderCopyEx;
renderer->RenderReadPixels = GL_RenderReadPixels;
renderer->RenderPresent = GL_RenderPresent;
renderer->DestroyTexture = GL_DestroyTexture;
renderer->DestroyRenderer = GL_DestroyRenderer;
renderer->GL_BindTexture = GL_BindTexture;
renderer->GL_UnbindTexture = GL_UnbindTexture;
renderer->info = GL_RenderDriver.info;
renderer->info.flags = (SDL_RENDERER_ACCELERATED | SDL_RENDERER_TARGETTEXTURE);
renderer->driverdata = data;
renderer->window = window;
data->context = SDL_GL_CreateContext(window);
if (!data->context) {
GL_DestroyRenderer(renderer);
return NULL;
}
if (SDL_GL_MakeCurrent(window, data->context) < 0) {
GL_DestroyRenderer(renderer);
return NULL;
}
if (GL_LoadFunctions(data) < 0) {
GL_DestroyRenderer(renderer);
return NULL;
}
#ifdef __MACOSX__
/* Enable multi-threaded rendering */
/* Disabled until Ryan finishes his VBO/PBO code...
CGLEnable(CGLGetCurrentContext(), kCGLCEMPEngine);
*/
#endif
if (flags & SDL_RENDERER_PRESENTVSYNC) {
SDL_GL_SetSwapInterval(1);
} else {
SDL_GL_SetSwapInterval(0);
}
if (SDL_GL_GetSwapInterval() > 0) {
renderer->info.flags |= SDL_RENDERER_PRESENTVSYNC;
}
/* Check for debug output support */
if (SDL_GL_GetAttribute(SDL_GL_CONTEXT_FLAGS, &value) == 0 &&
(value & SDL_GL_CONTEXT_DEBUG_FLAG)) {
data->debug_enabled = SDL_TRUE;
}
if (data->debug_enabled && SDL_GL_ExtensionSupported("GL_ARB_debug_output")) {
PFNGLDEBUGMESSAGECALLBACKARBPROC glDebugMessageCallbackARBFunc = (PFNGLDEBUGMESSAGECALLBACKARBPROC) SDL_GL_GetProcAddress("glDebugMessageCallbackARB");
data->GL_ARB_debug_output_supported = SDL_TRUE;
data->glGetPointerv(GL_DEBUG_CALLBACK_FUNCTION_ARB, (GLvoid **)&data->next_error_callback);
data->glGetPointerv(GL_DEBUG_CALLBACK_USER_PARAM_ARB, &data->next_error_userparam);
glDebugMessageCallbackARBFunc(GL_HandleDebugMessage, renderer);
/* Make sure our callback is called when errors actually happen */
data->glEnable(GL_DEBUG_OUTPUT_SYNCHRONOUS_ARB);
}
if (SDL_GL_ExtensionSupported("GL_ARB_texture_rectangle")
|| SDL_GL_ExtensionSupported("GL_EXT_texture_rectangle")) {
data->GL_ARB_texture_rectangle_supported = SDL_TRUE;
data->glGetIntegerv(GL_MAX_RECTANGLE_TEXTURE_SIZE_ARB, &value);
renderer->info.max_texture_width = value;
renderer->info.max_texture_height = value;
} else {
data->glGetIntegerv(GL_MAX_TEXTURE_SIZE, &value);
renderer->info.max_texture_width = value;
renderer->info.max_texture_height = value;
}
/* Check for multitexture support */
if (SDL_GL_ExtensionSupported("GL_ARB_multitexture")) {
data->glActiveTextureARB = (PFNGLACTIVETEXTUREARBPROC) SDL_GL_GetProcAddress("glActiveTextureARB");
if (data->glActiveTextureARB) {
data->GL_ARB_multitexture_supported = SDL_TRUE;
data->glGetIntegerv(GL_MAX_TEXTURE_UNITS_ARB, &data->num_texture_units);
}
}
/* Check for shader support */
hint = SDL_GetHint(SDL_HINT_RENDER_OPENGL_SHADERS);
if (!hint || *hint != '0') {
data->shaders = GL_CreateShaderContext();
}
SDL_LogInfo(SDL_LOG_CATEGORY_RENDER, "OpenGL shaders: %s",
data->shaders ? "ENABLED" : "DISABLED");
/* We support YV12 textures using 3 textures and a shader */
if (data->shaders && data->num_texture_units >= 3) {
renderer->info.texture_formats[renderer->info.num_texture_formats++] = SDL_PIXELFORMAT_YV12;
renderer->info.texture_formats[renderer->info.num_texture_formats++] = SDL_PIXELFORMAT_IYUV;
}
#ifdef __MACOSX__
renderer->info.texture_formats[renderer->info.num_texture_formats++] = SDL_PIXELFORMAT_UYVY;
#endif
if (SDL_GL_ExtensionSupported("GL_EXT_framebuffer_object")) {
data->GL_EXT_framebuffer_object_supported = SDL_TRUE;
data->glGenFramebuffersEXT = (PFNGLGENFRAMEBUFFERSEXTPROC)
SDL_GL_GetProcAddress("glGenFramebuffersEXT");
data->glDeleteFramebuffersEXT = (PFNGLDELETEFRAMEBUFFERSEXTPROC)
SDL_GL_GetProcAddress("glDeleteFramebuffersEXT");
data->glFramebufferTexture2DEXT = (PFNGLFRAMEBUFFERTEXTURE2DEXTPROC)
SDL_GL_GetProcAddress("glFramebufferTexture2DEXT");
data->glBindFramebufferEXT = (PFNGLBINDFRAMEBUFFEREXTPROC)
SDL_GL_GetProcAddress("glBindFramebufferEXT");
data->glCheckFramebufferStatusEXT = (PFNGLCHECKFRAMEBUFFERSTATUSEXTPROC)
SDL_GL_GetProcAddress("glCheckFramebufferStatusEXT");
renderer->info.flags |= SDL_RENDERER_TARGETTEXTURE;
}
data->framebuffers = NULL;
/* Set up parameters for rendering */
GL_ResetState(renderer);
return renderer;
}
GL_CreateRenderer()這個函數的代碼非常長。
在這里提取它最重點的幾個進行簡單的分析。
（1） 為SDL_Renderer分配內存
這一步比較簡單。
直接使用SDL_calloc()分配內存就能夠了。
（2） 渲染器接口函數賦值
SDL_Render結構體中有一系列的函數指針，包括了有關渲染器的各種功能。這一點在Direct3D的時候已經提過。不再反復。
代碼例如以下。
renderer->WindowEvent = GL_WindowEvent;
renderer->GetOutputSize = GL_GetOutputSize;
renderer->CreateTexture = GL_CreateTexture;
renderer->UpdateTexture = GL_UpdateTexture;
renderer->UpdateTextureYUV = GL_UpdateTextureYUV;
renderer->LockTexture = GL_LockTexture;
renderer->UnlockTexture = GL_UnlockTexture;
renderer->SetRenderTarget = GL_SetRenderTarget;
renderer->UpdateViewport = GL_UpdateViewport;
renderer->UpdateClipRect = GL_UpdateClipRect;
renderer->RenderClear = GL_RenderClear;
renderer->RenderDrawPoints = GL_RenderDrawPoints;
renderer->RenderDrawLines = GL_RenderDrawLines;
renderer->RenderFillRects = GL_RenderFillRects;
renderer->RenderCopy = GL_RenderCopy;
renderer->RenderCopyEx = GL_RenderCopyEx;
renderer->RenderReadPixels = GL_RenderReadPixels;
renderer->RenderPresent = GL_RenderPresent;
renderer->DestroyTexture = GL_DestroyTexture;
renderer->DestroyRenderer = GL_DestroyRenderer;
renderer->GL_BindTexture = GL_BindTexture;
renderer->GL_UnbindTexture = GL_UnbindTexture;
（3） 初始化OpenGL
初始化OpenGL各種變量，包括SDL_GL_CreateContext()，SDL_GL_MakeCurrent()，GL_LoadFunctions()等函數。這一部分還沒有具體分析。
（4） 初始化Shader
對Shader的初始化在函數GL_CreateShaderContext()中完畢。
GL_CreateShaderContext()的代碼例如以下（位于renderopenglSDL_shaders_gl.c）。
GL_ShaderContext * GL_CreateShaderContext()
{
GL_ShaderContext *ctx;
SDL_bool shaders_supported;
int i;
ctx = (GL_ShaderContext *)SDL_calloc(1, sizeof(*ctx));
if (!ctx) {
return NULL;
}
if (SDL_GL_ExtensionSupported("GL_ARB_texture_rectangle")
|| SDL_GL_ExtensionSupported("GL_EXT_texture_rectangle")) {
ctx->GL_ARB_texture_rectangle_supported = SDL_TRUE;
}
/* Check for shader support */
shaders_supported = SDL_FALSE;
if (SDL_GL_ExtensionSupported("GL_ARB_shader_objects") &&
SDL_GL_ExtensionSupported("GL_ARB_shading_language_100") &&
SDL_GL_ExtensionSupported("GL_ARB_vertex_shader") &&
SDL_GL_ExtensionSupported("GL_ARB_fragment_shader")) {
ctx->glGetError = (GLenum (*)(void)) SDL_GL_GetProcAddress("glGetError");
ctx->glAttachObjectARB = (PFNGLATTACHOBJECTARBPROC) SDL_GL_GetProcAddress("glAttachObjectARB");
ctx->glCompileShaderARB = (PFNGLCOMPILESHADERARBPROC) SDL_GL_GetProcAddress("glCompileShaderARB");
ctx->glCreateProgramObjectARB = (PFNGLCREATEPROGRAMOBJECTARBPROC) SDL_GL_GetProcAddress("glCreateProgramObjectARB");
ctx->glCreateShaderObjectARB = (PFNGLCREATESHADEROBJECTARBPROC) SDL_GL_GetProcAddress("glCreateShaderObjectARB");
ctx->glDeleteObjectARB = (PFNGLDELETEOBJECTARBPROC) SDL_GL_GetProcAddress("glDeleteObjectARB");
ctx->glGetInfoLogARB = (PFNGLGETINFOLOGARBPROC) SDL_GL_GetProcAddress("glGetInfoLogARB");
ctx->glGetObjectParameterivARB = (PFNGLGETOBJECTPARAMETERIVARBPROC) SDL_GL_GetProcAddress("glGetObjectParameterivARB");
ctx->glGetUniformLocationARB = (PFNGLGETUNIFORMLOCATIONARBPROC) SDL_GL_GetProcAddress("glGetUniformLocationARB");
ctx->glLinkProgramARB = (PFNGLLINKPROGRAMARBPROC) SDL_GL_GetProcAddress("glLinkProgramARB");
ctx->glShaderSourceARB = (PFNGLSHADERSOURCEARBPROC) SDL_GL_GetProcAddress("glShaderSourceARB");
ctx->glUniform1iARB = (PFNGLUNIFORM1IARBPROC) SDL_GL_GetProcAddress("glUniform1iARB");
ctx->glUniform1fARB = (PFNGLUNIFORM1FARBPROC) SDL_GL_GetProcAddress("glUniform1fARB");
ctx->glUseProgramObjectARB = (PFNGLUSEPROGRAMOBJECTARBPROC) SDL_GL_GetProcAddress("glUseProgramObjectARB");
if (ctx->glGetError &&
ctx->glAttachObjectARB &&
ctx->glCompileShaderARB &&
ctx->glCreateProgramObjectARB &&
ctx->glCreateShaderObjectARB &&
ctx->glDeleteObjectARB &&
ctx->glGetInfoLogARB &&
ctx->glGetObjectParameterivARB &&
ctx->glGetUniformLocationARB &&
ctx->glLinkProgramARB &&
ctx->glShaderSourceARB &&
ctx->glUniform1iARB &&
ctx->glUniform1fARB &&
ctx->glUseProgramObjectARB) {
shaders_supported = SDL_TRUE;
}
}
if (!shaders_supported) {
SDL_free(ctx);
return NULL;
}
/* Compile all the shaders */
for (i = 0; i < NUM_SHADERS; ++i) {
if (!CompileShaderProgram(ctx, i, &ctx->shaders[i])) {
GL_DestroyShaderContext(ctx);
return NULL;
}
}
/* We're done! */
return ctx;
}
上述代碼主要完畢了以下兩步：
第一步，初始化GL_ShaderContext。GL_ShaderContext中包括了OpenGL的Shader方面用到的各種接口函數。GL_ShaderContext定義例如以下。
struct GL_ShaderContext
{
GLenum (*glGetError)(void);
PFNGLATTACHOBJECTARBPROC glAttachObjectARB;
PFNGLCOMPILESHADERARBPROC glCompileShaderARB;
PFNGLCREATEPROGRAMOBJECTARBPROC glCreateProgramObjectARB;
PFNGLCREATESHADEROBJECTARBPROC glCreateShaderObjectARB;
PFNGLDELETEOBJECTARBPROC glDeleteObjectARB;
PFNGLGETINFOLOGARBPROC glGetInfoLogARB;
PFNGLGETOBJECTPARAMETERIVARBPROC glGetObjectParameterivARB;
PFNGLGETUNIFORMLOCATIONARBPROC glGetUniformLocationARB;
PFNGLLINKPROGRAMARBPROC glLinkProgramARB;
PFNGLSHADERSOURCEARBPROC glShaderSourceARB;
PFNGLUNIFORM1IARBPROC glUniform1iARB;
PFNGLUNIFORM1FARBPROC glUniform1fARB;
PFNGLUSEPROGRAMOBJECTARBPROC glUseProgramObjectARB;
SDL_bool GL_ARB_texture_rectangle_supported;
GL_ShaderData shaders[NUM_SHADERS];
};
看這個結構體的定義會給人一種非常混亂的感覺。
不用去理會那些大串的大寫字母，僅僅要知道這個結構體是函數的接口的“合集”就能夠了。
從函數的名稱中我們能夠看出有編譯Shader的glCreateShaderObject()，glShaderSource()，glCompileShader()等；以及編譯Program的glCreateProgramObject()。glAttachObject ()，glLinkProgram()，glUseProgramObject ()等等。
GL_CreateShaderContext()函數中創建了一個GL_ShaderContext并對當中的接口函數進行了賦值。
第二步，編譯Shader程序。該功能在CompileShaderProgram()函數中完畢。
CompileShaderProgram()的函數代碼例如以下所看到的。
static SDL_bool CompileShaderProgram(GL_ShaderContext *ctx, int index, GL_ShaderData *data)
{
const int num_tmus_bound = 4;
const char *vert_defines = "";
const char *frag_defines = "";
int i;
GLint location;
if (index == SHADER_NONE) {
return SDL_TRUE;
}
ctx->glGetError();
/* Make sure we use the correct sampler type for our texture type */
if (ctx->GL_ARB_texture_rectangle_supported) {
frag_defines =
"#define sampler2D sampler2DRect
"
"#define texture2D texture2DRect
";
}
/* Create one program object to rule them all */
data->program = ctx->glCreateProgramObjectARB();
/* Create the vertex shader */
data->vert_shader = ctx->glCreateShaderObjectARB(GL_VERTEX_SHADER_ARB);
if (!CompileShader(ctx, data->vert_shader, vert_defines, shader_source[index][0])) {
return SDL_FALSE;
}
/* Create the fragment shader */
data->frag_shader = ctx->glCreateShaderObjectARB(GL_FRAGMENT_SHADER_ARB);
if (!CompileShader(ctx, data->frag_shader, frag_defines, shader_source[index][1])) {
return SDL_FALSE;
}
/* ... and in the darkness bind them */
ctx->glAttachObjectARB(data->program, data->vert_shader);
ctx->glAttachObjectARB(data->program, data->frag_shader);
ctx->glLinkProgramARB(data->program);
/* Set up some uniform variables */
ctx->glUseProgramObjectARB(data->program);
for (i = 0; i < num_tmus_bound; ++i) {
char tex_name[10];
SDL_snprintf(tex_name, SDL_arraysize(tex_name), "tex%d", i);
location = ctx->glGetUniformLocationARB(data->program, tex_name);
if (location >= 0) {
ctx->glUniform1iARB(location, i);
}
}
ctx->glUseProgramObjectARB(0);
return (ctx->glGetError() == GL_NO_ERROR);
}
從代碼中能夠看出。這個函數調用了GL_ShaderContext中用于初始化Shader以及Program的各個函數。有關初始化的流程不再細說，能夠參考相關的文章。
在該函數中，調用了CompileShader()專門用于初始化Shader。
該函數被調用了兩次，分別用于初始化vertex shader和fragment shader。
CompileShader()的代碼例如以下。
static SDL_bool CompileShader(GL_ShaderContext *ctx, GLhandleARB shader, const char *defines, const char *source)
{
GLint status;
const char *sources[2];
sources[0] = defines;
sources[1] = source;
ctx->glShaderSourceARB(shader, SDL_arraysize(sources), sources, NULL);
ctx->glCompileShaderARB(shader);
ctx->glGetObjectParameterivARB(shader, GL_OBJECT_COMPILE_STATUS_ARB, &status);
if (status == 0) {
GLint length;
char *info;
ctx->glGetObjectParameterivARB(shader, GL_OBJECT_INFO_LOG_LENGTH_ARB, &length);
info = SDL_stack_alloc(char, length+1);
ctx->glGetInfoLogARB(shader, length, NULL, info);
SDL_LogError(SDL_LOG_CATEGORY_RENDER,
"Failed to compile shader:
%s%s
%s", defines, source, info);
#ifdef DEBUG_SHADERS
fprintf(stderr,
"Failed to compile shader:
%s%s
%s", defines, source, info);
#endif
SDL_stack_free(info);
return SDL_FALSE;
} else {
return SDL_TRUE;
}
}
從代碼中能夠看出，該函數調用glShaderSource()。glCompileShader()。glGetObjectParameteriv()這幾個函數初始化一個Shader。
Shader的代碼位于一個名稱為shader_source的char型二維數組里。源碼例如以下所看到的。
數組中每一個元素代表一個Shader的代碼，每一個Shader的代碼包括兩個部分：vertex shader代碼（相應元素[0]）以及fragment shader代碼（相應元素[1]）。
/*
* NOTE: Always use sampler2D, etc here. We'll #define them to the
* texture_rectangle versions if we choose to use that extension.
*/
static const char *shader_source[NUM_SHADERS][2] =
{
/* SHADER_NONE */
{ NULL, NULL },
/* SHADER_SOLID */
{
/* vertex shader */
"varying vec4 v_color;
"
"
"
"void main()
"
"{
"
" gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
"
" v_color = gl_Color;
"
"}",
/* fragment shader */
"varying vec4 v_color;
"
"
"
"void main()
"
"{
"
" gl_FragColor = v_color;
"
"}"
},
/* SHADER_RGB */
{
/* vertex shader */
"varying vec4 v_color;
"
"varying vec2 v_texCoord;
"
"
"
"void main()
"
"{
"
" gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
"
" v_color = gl_Color;
"
" v_texCoord = vec2(gl_MultiTexCoord0);
"
"}",
/* fragment shader */
"varying vec4 v_color;
"
"varying vec2 v_texCoord;
"
"uniform sampler2D tex0;
"
"
"
"void main()
"
"{
"
" gl_FragColor = texture2D(tex0, v_texCoord) * v_color;
"
"}"
},
/* SHADER_YV12 */
{
/* vertex shader */
"varying vec4 v_color;
"
"varying vec2 v_texCoord;
"
"
"
"void main()
"
"{
"
" gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
"
" v_color = gl_Color;
"
" v_texCoord = vec2(gl_MultiTexCoord0);
"
"}",
/* fragment shader */
"varying vec4 v_color;
"
"varying vec2 v_texCoord;
"
"uniform sampler2D tex0; // Y
"
"uniform sampler2D tex1; // U
"
"uniform sampler2D tex2; // V
"
"
"
"// YUV offset
"
"const vec3 offset = vec3(-0.0625, -0.5, -0.5);
"
"
"
"// RGB coefficients
"
"const vec3 Rcoeff = vec3(1.164, 0.000, 1.596);
"
"const vec3 Gcoeff = vec3(1.164, -0.391, -0.813);
"
"const vec3 Bcoeff = vec3(1.164, 2.018, 0.000);
"
"
"
"void main()
"
"{
"
" vec2 tcoord;
"
" vec3 yuv, rgb;
"
"
"
" // Get the Y value
"
" tcoord = v_texCoord;
"
" yuv.x = texture2D(tex0, tcoord).r;
"
"
"
" // Get the U and V values
"
" tcoord *= 0.5;
"
" yuv.y = texture2D(tex1, tcoord).r;
"
" yuv.z = texture2D(tex2, tcoord).r;
"
"
"
" // Do the color transform
"
" yuv += offset;
"
" rgb.r = dot(yuv, Rcoeff);
"
" rgb.g = dot(yuv, Gcoeff);
"
" rgb.b = dot(yuv, Bcoeff);
"
"
"
" // That was easy. :)
"
" gl_FragColor = vec4(rgb, 1.0) * v_color;
"
"}"
},
};
有關OpenGL的渲染器的初始化代碼臨時分析到這里。
3. Software
Software的渲染器在創建函數是SW_CreateRenderer()。該函數位于rendersoftwareSDL_render_sw.c文件里。首先看一下它的代碼。
SDL_Renderer * SW_CreateRenderer(SDL_Window * window, Uint32 flags)
{
SDL_Surface *surface;
surface = SDL_GetWindowSurface(window);
if (!surface) {
return NULL;
}
return SW_CreateRendererForSurface(surface);
}
從代碼中能夠看出，SW_CreateRenderer()調用了2個函數：SDL_GetWindowSurface()和SW_CreateRendererForSurface()。SDL_GetWindowSurface()用于創建一個Surface；SW_CreateRendererForSurface()基于Surface創建一個Renderer。
以下分別看一下這2個函數的代碼。
SDL_GetWindowSurface()的代碼例如以下所看到的（位于videoSDL_video.c）。
SDL_Surface * SDL_GetWindowSurface(SDL_Window * window)
{
CHECK_WINDOW_MAGIC(window, NULL);
if (!window->surface_valid) {
if (window->surface) {
window->surface->flags &= ~SDL_DONTFREE;
SDL_FreeSurface(window->surface);
}
window->surface = SDL_CreateWindowFramebuffer(window);
if (window->surface) {
window->surface_valid = SDL_TRUE;
window->surface->flags |= SDL_DONTFREE;
}
}
return window->surface;
}
當中調用了一個函數SDL_CreateWindowFramebuffer()?？匆幌略摵瘮档拇a。
static SDL_Surface * SDL_CreateWindowFramebuffer(SDL_Window * window)
{
Uint32 format;
void *pixels;
int pitch;
int bpp;
Uint32 Rmask, Gmask, Bmask, Amask;
if (!_this->CreateWindowFramebuffer || !_this->UpdateWindowFramebuffer) {
return NULL;
}
if (_this->CreateWindowFramebuffer(_this, window, &format, &pixels, &pitch) < 0) {
return NULL;
}
if (!SDL_PixelFormatEnumToMasks(format, &bpp, &Rmask, &Gmask, &Bmask, &Amask)) {
return NULL;
}
return SDL_CreateRGBSurfaceFrom(pixels, window->w, window->h, bpp, pitch, Rmask, Gmask, Bmask, Amask);
}
該函數中調用了SDL_VideoDevice中的一個函數CreateWindowFramebuffer()。
我們以“Windows視頻驅動”為例，看看CreateWindowFramebuffer()中的代碼。在“Windows視頻驅動”下，CreateWindowFramebuffer()相應的函數是WIN_CreateWindowFramebuffer()。
以下看一下該函數的代碼。
int WIN_CreateWindowFramebuffer(_THIS, SDL_Window * window, Uint32 * format, void ** pixels, int *pitch)
{
SDL_WindowData *data = (SDL_WindowData *) window->driverdata;
size_t size;
LPBITMAPINFO info;
HBITMAP hbm;
/* Free the old framebuffer surface */
if (data->mdc) {
DeleteDC(data->mdc);
}
if (data->hbm) {
DeleteObject(data->hbm);
}
/* Find out the format of the screen */
size = sizeof(BITMAPINFOHEADER) + 256 * sizeof (RGBQUAD);
info = (LPBITMAPINFO)SDL_stack_alloc(Uint8, size);
SDL_memset(info, 0, size);
info->bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
/* The second call to GetDIBits() fills in the bitfields */
hbm = CreateCompatibleBitmap(data->hdc, 1, 1);
GetDIBits(data->hdc, hbm, 0, 0, NULL, info, DIB_RGB_COLORS);
GetDIBits(data->hdc, hbm, 0, 0, NULL, info, DIB_RGB_COLORS);
DeleteObject(hbm);
*format = SDL_PIXELFORMAT_UNKNOWN;
if (info->bmiHeader.biCompression == BI_BITFIELDS) {
int bpp;
Uint32 *masks;
bpp = info->bmiHeader.biPlanes * info->bmiHeader.biBitCount;
masks = (Uint32*)((Uint8*)info + info->bmiHeader.biSize);
*format = SDL_MasksToPixelFormatEnum(bpp, masks[0], masks[1], masks[2], 0);
}
if (*format == SDL_PIXELFORMAT_UNKNOWN)
{
/* We'll use RGB format for now */
*format = SDL_PIXELFORMAT_RGB888;
/* Create a new one */
SDL_memset(info, 0, size);
info->bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
info->bmiHeader.biPlanes = 1;
info->bmiHeader.biBitCount = 32;
info->bmiHeader.biCompression = BI_RGB;
}
/* Fill in the size information */
*pitch = (((window->w * SDL_BYTESPERPIXEL(*format)) + 3) & ~3);
info->bmiHeader.biWidth = window->w;
info->bmiHeader.biHeight = -window->h; /* negative for topdown bitmap */
info->bmiHeader.biSizeImage = window->h * (*pitch);
data->mdc = CreateCompatibleDC(data->hdc);
data->hbm = CreateDIBSection(data->hdc, info, DIB_RGB_COLORS, pixels, NULL, 0);
SDL_stack_free(info);
if (!data->hbm) {
return WIN_SetError("Unable to create DIB");
}
SelectObject(data->mdc, data->hbm);
return 0;
}
從代碼中能夠看出，該函數調用了Win32的API函數CreateCompatibleBitmap()，CreateCompatibleDC()等一系列方法創建了“Surface”。
SDL_GetWindowSurface()函數到此分析完畢，如今回過頭來再看SW_CreateRenderer ()的還有一個函數SW_CreateRendererForSurface()。
該函數的代碼例如以下。
SDL_Renderer * SW_CreateRendererForSurface(SDL_Surface * surface)
{
SDL_Renderer *renderer;
SW_RenderData *data;
if (!surface) {
SDL_SetError("Can't create renderer for NULL surface");
return NULL;
}
renderer = (SDL_Renderer *) SDL_calloc(1, sizeof(*renderer));
if (!renderer) {
SDL_OutOfMemory();
return NULL;
}
data = (SW_RenderData *) SDL_calloc(1, sizeof(*data));
if (!data) {
SW_DestroyRenderer(renderer);
SDL_OutOfMemory();
return NULL;
}
data->surface = surface;
renderer->WindowEvent = SW_WindowEvent;
renderer->GetOutputSize = SW_GetOutputSize;
renderer->CreateTexture = SW_CreateTexture;
renderer->SetTextureColorMod = SW_SetTextureColorMod;
renderer->SetTextureAlphaMod = SW_SetTextureAlphaMod;
renderer->SetTextureBlendMode = SW_SetTextureBlendMode;
renderer->UpdateTexture = SW_UpdateTexture;
renderer->LockTexture = SW_LockTexture;
renderer->UnlockTexture = SW_UnlockTexture;
renderer->SetRenderTarget = SW_SetRenderTarget;
renderer->UpdateViewport = SW_UpdateViewport;
renderer->UpdateClipRect = SW_UpdateClipRect;
renderer->RenderClear = SW_RenderClear;
renderer->RenderDrawPoints = SW_RenderDrawPoints;
renderer->RenderDrawLines = SW_RenderDrawLines;
renderer->RenderFillRects = SW_RenderFillRects;
renderer->RenderCopy = SW_RenderCopy;
renderer->RenderCopyEx = SW_RenderCopyEx;
renderer->RenderReadPixels = SW_RenderReadPixels;
renderer->RenderPresent = SW_RenderPresent;
renderer->DestroyTexture = SW_DestroyTexture;
renderer->DestroyRenderer = SW_DestroyRenderer;
renderer->info = SW_RenderDriver.info;
renderer->driverdata = data;
SW_ActivateRenderer(renderer);
return renderer;
}
與前面的函數一樣，該函數完畢了SDL_Renderer結構體中函數指針的賦值。
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