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SDL2源代码分析6：复制到渲染器（SDL_RenderCopy()）
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SDL源代码分析系列文章列表：
SDL2源代码分析1：初始化（SDL_Init()）
SDL2源代码分析2：窗口（SDL_Window）
SDL2源代码分析3：渲染器（SDL_Renderer）
SDL2源代码分析4：纹理（SDL_Texture）
SDL2源代码分析5：更新纹理（SDL_UpdateTexture()）
SDL2源代码分析6：复制到渲染器（SDL_RenderCopy()）
SDL2源代码分析7：显示（SDL_RenderPresent()）
SDL2源代码分析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的源代码。本文分析SDL纹理复制到渲染目标的函数SDL_RenderCopy()。
SDL播放视频的代码流程如下所示。
初始化:
SDL_Init(): 初始化SDL。
SDL_CreateWindow(): 创建窗口（Window）。
SDL_CreateRenderer(): 基于窗口创建渲染器（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()函数简介
SDL使用SDL_RenderCopy()将纹理数据复制给渲染目标。SDL_RenderCopy()的原型如下。
int SDLCALL SDL_RenderCopy(SDL_Renderer * renderer, SDL_Texture * texture, const SDL_Rect * srcrect, const SDL_Rect * dstrect);
参数的含义如下。
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可以用下图表示。
上面的图片不太清晰，更清晰的图片上传到了相册里面：
http://my.csdn.net/leixiaohua1020/album/detail/1793911
把相册里面的图片保存下来就可以得到清晰的图片了。
源代码分析
SDL_RenderCopy()的源代码位于render\SDL_render.c中，如下所示。
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);}
从源代码中可以看出，SDL_RenderCopy()的大致流程如下。
1.检查输入参数的合理性。
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。
下面我们详细看一下几种不同的渲染器的RenderCopy()的方法。
1.Direct3D
Direct3D 渲染器中对应RenderCopy()的函数是D3D_RenderCopy()，它的源代码如下所示（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;}
从代码中可以看出，D3D_RenderCopy()函数按照执行的顺序调用了如下函数：
D3D_ActivateRenderer()：激活渲染器。其内部使用Direct3D的API函数IDirect3DDevice9_BeginScene()开始一个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()：设置纹理采样方式。其内部调用使用Direct3D的API函数IDirect3DDevice9_SetSamplerState()设置D3D的纹理采样方式。
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()：设置纹理采样方式。
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渲染器中对应RenderCopy()的函数是GL_RenderCopy()，它的源代码如下所示（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);}
从代码中可以看出，GL_RenderCopy()函数调用了OpenGL的API函数glActiveTexture()，glBindTexture()创建了一个纹理。并且使用GL_SetBlendMode()，GL_SetShader()设置了有关的一些参数。
有一点需要注意，在OpenGL渲染器中，如果输入像素格式是YUV，就会使用3个纹理。
3.Software
Software渲染器中对应RenderCopy()的函数是SW_RenderCopy()，它的源代码如下所示（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); }}
该函数的源代码还没有详细分析。
