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SDL源码分析系列文章列表：

SDL2源码分析1：初始化（SDL_Init()）

SDL2源码分析2：窗体（SDL_Window）

SDL2源码分析3：渲染器（SDL_Renderer）

SDL2源码分析4：纹理（SDL_Texture）

SDL2源码分析5：更新纹理（SDL_UpdateTexture()）

SDL2源码分析6：拷贝到渲染器（SDL_RenderCopy()）

SDL2源码分析7：显示（SDL_RenderPresent()）

SDL2源码分析8：视频显示总结

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上一篇文章分析了SDL更新纹理像素数据的函数SDL_UpdateTexture()。这篇文章继续分析SDL的源码。本文分析SDL纹理拷贝到渲染目标的函数SDL_RenderCopy()。

SDL播放视频的代码流程例如以下所看到的。

初始化: 

SDL_Init(): 初始化SDL。 
SDL_CreateWindow(): 创建窗体（Window）。 
SDL_CreateRenderer(): 基于窗体创建渲染器（Render）。 
SDL_CreateTexture(): 创建纹理（Texture）。

循环渲染数据: 

SDL_UpdateTexture(): 设置纹理的数据。 
SDL_RenderCopy(): 纹理复制给渲染器。 
SDL_RenderPresent(): 显示。

上篇文章分析了该流程中的第5个函数SDL_UpdateTexture()。本文继续分析该流程中的第6个函数SDL_RenderCopy()。

SDL_RenderCopy()

函数简单介绍

SDL使用SDL_RenderCopy()将纹理数据复制给渲染目标。SDL_RenderCopy()的原型例如以下。

int SDLCALL SDL_RenderCopy(SDL_Renderer * renderer,SDL_Texture * texture,const SDL_Rect * srcrect,const SDL_Rect * dstrect);

參数的含义例如以下。
renderer：渲染目标。
texture：输入纹理。
srcrect：选择输入纹理的一块矩形区域作为输入。设置为NULL的时候整个纹理作为输入。
dstrect：选择渲染目标的一块矩形区域作为输出。设置为NULL的时候整个渲染目标作为输出。

成功的话返回0，失败的话返回-1。

函数调用关系图

SDL_RenderCopy()关键函数的调用关系能够用下图表示。

上面的图片不太清晰，更清晰的图片上传到了相冊里面：

http://my.csdn.net/leixiaohua1020/album/detail/1793911

把相冊里面的图片保存下来就能够得到清晰的图片了。

源码分析

SDL_RenderCopy()的源码位于render\SDL_render.c中。例如以下所看到的。

int SDL_RenderCopy(SDL_Renderer * renderer, SDL_Texture * texture,const SDL_Rect * srcrect, const SDL_Rect * dstrect)
{SDL_Rect real_srcrect = { 0, 0, 0, 0 };SDL_Rect real_dstrect = { 0, 0, 0, 0 };SDL_FRect frect;CHECK_RENDERER_MAGIC(renderer, -1);CHECK_TEXTURE_MAGIC(texture, -1);if (renderer != texture->renderer) {return SDL_SetError("Texture was not created with this renderer");}real_srcrect.x = 0;real_srcrect.y = 0;real_srcrect.w = texture->w;real_srcrect.h = texture->h;if (srcrect) {if (!SDL_IntersectRect(srcrect, &real_srcrect, &real_srcrect)) {return 0;}}SDL_RenderGetViewport(renderer, &real_dstrect);real_dstrect.x = 0;real_dstrect.y = 0;if (dstrect) {if (!SDL_HasIntersection(dstrect, &real_dstrect)) {return 0;}real_dstrect = *dstrect;}if (texture->native) {texture = texture->native;}/* Don't draw while we're hidden */if (renderer->hidden) {return 0;}frect.x = real_dstrect.x * renderer->scale.x;frect.y = real_dstrect.y * renderer->scale.y;frect.w = real_dstrect.w * renderer->scale.x;frect.h = real_dstrect.h * renderer->scale.y;return renderer->RenderCopy(renderer, texture, &real_srcrect, &frect);
}

从源码中能够看出，SDL_RenderCopy()的大致流程例如以下。

1. 检查输入參数的合理性。
2. 调用SDL_Render的RenderCopy ()方法复制纹理到渲染目标。这一步是整个函数的核心。

以下我们具体看一下几种不同的渲染器的RenderCopy()的方法。

1. Direct3D

Direct3D 渲染器中相应RenderCopy()的函数是D3D_RenderCopy()，它的源码例如以下所看到的（位于render\direct3d\SDL_render_d3d.c）。

static int D3D_RenderCopy(SDL_Renderer * renderer, SDL_Texture * texture,const SDL_Rect * srcrect, const SDL_FRect * dstrect)
{D3D_RenderData *data = (D3D_RenderData *) renderer->driverdata;D3D_TextureData *texturedata;LPDIRECT3DPIXELSHADER9 shader = NULL;float minx, miny, maxx, maxy;float minu, maxu, minv, maxv;DWORD color;Vertex vertices[4];HRESULT result;if (D3D_ActivateRenderer(renderer) < 0) {return -1;}texturedata = (D3D_TextureData *)texture->driverdata;if (!texturedata) {SDL_SetError("Texture is not currently available");return -1;}minx = dstrect->x - 0.5f;miny = dstrect->y - 0.5f;maxx = dstrect->x + dstrect->w - 0.5f;maxy = dstrect->y + dstrect->h - 0.5f;minu = (float) srcrect->x / texture->w;maxu = (float) (srcrect->x + srcrect->w) / texture->w;minv = (float) srcrect->y / texture->h;maxv = (float) (srcrect->y + srcrect->h) / texture->h;color = D3DCOLOR_ARGB(texture->a, texture->r, texture->g, texture->b);vertices[0].x = minx;vertices[0].y = miny;vertices[0].z = 0.0f;vertices[0].color = color;vertices[0].u = minu;vertices[0].v = minv;vertices[1].x = maxx;vertices[1].y = miny;vertices[1].z = 0.0f;vertices[1].color = color;vertices[1].u = maxu;vertices[1].v = minv;vertices[2].x = maxx;vertices[2].y = maxy;vertices[2].z = 0.0f;vertices[2].color = color;vertices[2].u = maxu;vertices[2].v = maxv;vertices[3].x = minx;vertices[3].y = maxy;vertices[3].z = 0.0f;vertices[3].color = color;vertices[3].u = minu;vertices[3].v = maxv;D3D_SetBlendMode(data, texture->blendMode);D3D_UpdateTextureScaleMode(data, texturedata, 0);result =IDirect3DDevice9_SetTexture(data->device, 0, (IDirect3DBaseTexture9 *)texturedata->texture);if (FAILED(result)) {return D3D_SetError("SetTexture()", result);}if (texturedata->yuv) {shader = data->ps_yuv;D3D_UpdateTextureScaleMode(data, texturedata, 1);D3D_UpdateTextureScaleMode(data, texturedata, 2);result =IDirect3DDevice9_SetTexture(data->device, 1, (IDirect3DBaseTexture9 *)texturedata->utexture);if (FAILED(result)) {return D3D_SetError("SetTexture()", result);}result =IDirect3DDevice9_SetTexture(data->device, 2, (IDirect3DBaseTexture9 *)texturedata->vtexture);if (FAILED(result)) {return D3D_SetError("SetTexture()", result);}}if (shader) {result = IDirect3DDevice9_SetPixelShader(data->device, shader);if (FAILED(result)) {return D3D_SetError("SetShader()", result);}}result =IDirect3DDevice9_DrawPrimitiveUP(data->device, D3DPT_TRIANGLEFAN, 2,vertices, sizeof(*vertices));if (FAILED(result)) {return D3D_SetError("DrawPrimitiveUP()", result);}if (shader) {result = IDirect3DDevice9_SetPixelShader(data->device, NULL);if (FAILED(result)) {return D3D_SetError("SetShader()", result);}}return 0;
}

从代码中能够看出，D3D_RenderCopy()函数依照运行的顺序调用了例如以下函数：

D3D_ActivateRenderer()：激活渲染器。

其内部使用Direct3D的API函数IDirect3DDevice9_BeginScene()開始一个D3D的场景。
D3D_SetBlendMode()：设置渲染器状态。

其内部使用Direct3D的API函数IDirect3DDevice9_SetRenderState()设置渲染器的状态。

D3D_UpdateTextureScaleMode()：设置纹理採样方式。其内部调用使用Direct3D的API函数IDirect3DDevice9_SetSamplerState()设置D3D的纹理採样方式。
IDirect3DDevice9_SetTexture()：Direct3D的API。用于设置当前启用的纹理。
IDirect3DDevice9_SetPixelShader()：Direct3D的API。用于设置使用的像素着色器。

IDirect3DDevice9_DrawPrimitiveUP()：Direct3D的API，用于渲染。

上述几个函数中，前3个函数是SDL中的函数，后3个函数是Direct3D的API。

在此附上前三个函数的代码。

D3D_ActivateRenderer()：激活渲染器。

static int D3D_ActivateRenderer(SDL_Renderer * renderer)
{D3D_RenderData *data = (D3D_RenderData *) renderer->driverdata;HRESULT result;if (data->updateSize) {SDL_Window *window = renderer->window;int w, h;SDL_GetWindowSize(window, &w, &h);data->pparams.BackBufferWidth = w;data->pparams.BackBufferHeight = h;if (SDL_GetWindowFlags(window) & SDL_WINDOW_FULLSCREEN) {data->pparams.BackBufferFormat =PixelFormatToD3DFMT(SDL_GetWindowPixelFormat(window));} else {data->pparams.BackBufferFormat = D3DFMT_UNKNOWN;}if (D3D_Reset(renderer) < 0) {return -1;}data->updateSize = SDL_FALSE;}if (data->beginScene) {result = IDirect3DDevice9_BeginScene(data->device);if (result == D3DERR_DEVICELOST) {if (D3D_Reset(renderer) < 0) {return -1;}result = IDirect3DDevice9_BeginScene(data->device);}if (FAILED(result)) {return D3D_SetError("BeginScene()", result);}data->beginScene = SDL_FALSE;}return 0;
}

D3D_SetBlendMode()：设置渲染器状态。

static void D3D_SetBlendMode(D3D_RenderData * data, int blendMode)
{switch (blendMode) {case SDL_BLENDMODE_NONE:IDirect3DDevice9_SetRenderState(data->device, D3DRS_ALPHABLENDENABLE,FALSE);break;case SDL_BLENDMODE_BLEND:IDirect3DDevice9_SetRenderState(data->device, D3DRS_ALPHABLENDENABLE,TRUE);IDirect3DDevice9_SetRenderState(data->device, D3DRS_SRCBLEND,D3DBLEND_SRCALPHA);IDirect3DDevice9_SetRenderState(data->device, D3DRS_DESTBLEND,D3DBLEND_INVSRCALPHA);if (data->enableSeparateAlphaBlend) {IDirect3DDevice9_SetRenderState(data->device, D3DRS_SRCBLENDALPHA,D3DBLEND_ONE);IDirect3DDevice9_SetRenderState(data->device, D3DRS_DESTBLENDALPHA,D3DBLEND_INVSRCALPHA);}break;case SDL_BLENDMODE_ADD:IDirect3DDevice9_SetRenderState(data->device, D3DRS_ALPHABLENDENABLE,TRUE);IDirect3DDevice9_SetRenderState(data->device, D3DRS_SRCBLEND,D3DBLEND_SRCALPHA);IDirect3DDevice9_SetRenderState(data->device, D3DRS_DESTBLEND,D3DBLEND_ONE);if (data->enableSeparateAlphaBlend) {IDirect3DDevice9_SetRenderState(data->device, D3DRS_SRCBLENDALPHA,D3DBLEND_ZERO);IDirect3DDevice9_SetRenderState(data->device, D3DRS_DESTBLENDALPHA,D3DBLEND_ONE);}break;case SDL_BLENDMODE_MOD:IDirect3DDevice9_SetRenderState(data->device, D3DRS_ALPHABLENDENABLE,TRUE);IDirect3DDevice9_SetRenderState(data->device, D3DRS_SRCBLEND,D3DBLEND_ZERO);IDirect3DDevice9_SetRenderState(data->device, D3DRS_DESTBLEND,D3DBLEND_SRCCOLOR);if (data->enableSeparateAlphaBlend) {IDirect3DDevice9_SetRenderState(data->device, D3DRS_SRCBLENDALPHA,D3DBLEND_ZERO);IDirect3DDevice9_SetRenderState(data->device, D3DRS_DESTBLENDALPHA,D3DBLEND_ONE);}break;}
}

D3D_UpdateTextureScaleMode()：设置纹理採样方式。

static void D3D_UpdateTextureScaleMode(D3D_RenderData *data, D3D_TextureData *texturedata, unsigned index)
{if (texturedata->scaleMode != data->scaleMode[index]) {IDirect3DDevice9_SetSamplerState(data->device, index, D3DSAMP_MINFILTER,texturedata->scaleMode);IDirect3DDevice9_SetSamplerState(data->device, index, D3DSAMP_MAGFILTER,texturedata->scaleMode);data->scaleMode[index] = texturedata->scaleMode;}
}

2. OpenGL

OpenGL渲染器中相应RenderCopy()的函数是GL_RenderCopy()，它的源码例如以下所看到的（位于render\opengl\SDL_render_gl.c）。

static int GL_RenderCopy(SDL_Renderer * renderer, SDL_Texture * texture,const SDL_Rect * srcrect, const SDL_FRect * dstrect)
{GL_RenderData *data = (GL_RenderData *) renderer->driverdata;GL_TextureData *texturedata = (GL_TextureData *) texture->driverdata;GLfloat minx, miny, maxx, maxy;GLfloat minu, maxu, minv, maxv;GL_ActivateRenderer(renderer);data->glEnable(texturedata->type);if (texturedata->yuv) {data->glActiveTextureARB(GL_TEXTURE2_ARB);data->glBindTexture(texturedata->type, texturedata->vtexture);data->glActiveTextureARB(GL_TEXTURE1_ARB);data->glBindTexture(texturedata->type, texturedata->utexture);data->glActiveTextureARB(GL_TEXTURE0_ARB);}data->glBindTexture(texturedata->type, texturedata->texture);if (texture->modMode) {GL_SetColor(data, texture->r, texture->g, texture->b, texture->a);} else {GL_SetColor(data, 255, 255, 255, 255);}GL_SetBlendMode(data, texture->blendMode);if (texturedata->yuv) {GL_SetShader(data, SHADER_YV12);} else {GL_SetShader(data, SHADER_RGB);}minx = dstrect->x;miny = dstrect->y;maxx = dstrect->x + dstrect->w;maxy = dstrect->y + dstrect->h;minu = (GLfloat) srcrect->x / texture->w;minu *= texturedata->texw;maxu = (GLfloat) (srcrect->x + srcrect->w) / texture->w;maxu *= texturedata->texw;minv = (GLfloat) srcrect->y / texture->h;minv *= texturedata->texh;maxv = (GLfloat) (srcrect->y + srcrect->h) / texture->h;maxv *= texturedata->texh;data->glBegin(GL_TRIANGLE_STRIP);data->glTexCoord2f(minu, minv);data->glVertex2f(minx, miny);data->glTexCoord2f(maxu, minv);data->glVertex2f(maxx, miny);data->glTexCoord2f(minu, maxv);data->glVertex2f(minx, maxy);data->glTexCoord2f(maxu, maxv);data->glVertex2f(maxx, maxy);data->glEnd();data->glDisable(texturedata->type);return GL_CheckError("", renderer);
}

从代码中能够看出。GL_RenderCopy()函数调用了OpenGL的API函数glActiveTexture()，glBindTexture()创建了一个纹理。而且使用GL_SetBlendMode()，GL_SetShader()设置了有关的一些參数。

有一点须要注意，在OpenGL渲染器中。假设输入像素格式是YUV，就会使用3个纹理。

3. Software

Software渲染器中相应RenderCopy()的函数是SW_RenderCopy()。它的源码例如以下所看到的（位于render\software\SDL_render_sw.c）。

static int SW_RenderCopy(SDL_Renderer * renderer, SDL_Texture * texture,const SDL_Rect * srcrect, const SDL_FRect * dstrect)
{SDL_Surface *surface = SW_ActivateRenderer(renderer);SDL_Surface *src = (SDL_Surface *) texture->driverdata;SDL_Rect final_rect;if (!surface) {return -1;}if (renderer->viewport.x || renderer->viewport.y) {final_rect.x = (int)(renderer->viewport.x + dstrect->x);final_rect.y = (int)(renderer->viewport.y + dstrect->y);} else {final_rect.x = (int)dstrect->x;final_rect.y = (int)dstrect->y;}final_rect.w = (int)dstrect->w;final_rect.h = (int)dstrect->h;if ( srcrect->w == final_rect.w && srcrect->h == final_rect.h ) {return SDL_BlitSurface(src, srcrect, surface, &final_rect);} else {return SDL_BlitScaled(src, srcrect, surface, &final_rect);}
}

该函数的源码还没有具体分析。