c - 确定 SDL_CreateTexture() 的正确像素格式？

Question

我正在努力将一个简单的乒乓球游戏从 SDL 转换为 SDL2，因为我找不到像素格式参数的有效值(第二个参数“Uint32 格式”) 当调用 SDL_CreateTexture() 时。最后，我通过使用 SDL_PIXELFORMAT_ARGB8888 获得了成功，而且我还发现 SDL_PIXELFORMAT_UNKNOWN 也能正常工作。然而，在阅读了几篇关于系统字节顺序和确定字节顺序的文章后，我仍然不确定如何在不猜测、使用未知或运行一些单独的 shell 脚本的情况下为给定系统找到有效的像素格式。

仅依赖 SDL_PIXELFORMAT_UNKNOWN 是否安全？谁能提供一些信息(或链接)来帮助我更好地理解这些概念并实现它们？为了以后的图形编程，我想更好地理解相关概念。

这是代码最初的样子:

screen = SDL_CreateRGBSurfaceWithFormat(0, width, height, 32, 
                                        SDL_PIXELTYPE_RGBA32); 

screen_texture = SDL_CreateTextureFromSurface(renderer, screen);

以及我用来让它工作的东西:

screen = SDL_CreateRGBSurface(0, 640, 480, 32,
                              0x00FF0000,
                              0x0000FF00,
                              0x000000FF,
                              0xFF000000);

screen_texture = SDL_CreateTexture(renderer,
                                   SDL_PIXELFORMAT_ARGB8888, 
                                   SDL_TEXTUREACCESS_TARGET,
                                   640, 480); // SDL_PIXELFORMAT_UNKNOWN also works

Answer 1

给定的 SDL_Renderer 将支持至少一个 SDL_PixelFormatEnum；其他格式也可以，但可能会在创建和/或使用时产生转换损失。

使用 SDL_GetRendererInfo() 填充 SDL_RendererInfo 并使用 SDL_RendererInfo::texture_formats 中的一种格式(来自 here ):

SDL_RendererInfo info;
SDL_GetRendererInfo( renderer, &info );
cout << "Renderer name: " << info.name << endl;
cout << "Texture formats: " << endl;
for( Uint32 i = 0; i < info.num_texture_formats; i++ )
{
    cout << SDL_GetPixelFormatName( info.texture_formats[i] ) << endl;
}

当我运行时，DirectX 和 OpenGL 后端都支持 SDL_PIXELFORMAT_ARGB8888。

通过 git grep -A 25 SDL_RenderDriver 仔细检查 SDL 代码我认为第一个 texture_formats 是“首选”格式:

SDL_render_d3d.c:SDL_RenderDriver D3D_RenderDriver = {
SDL_render_d3d.c-    D3D_CreateRenderer,
SDL_render_d3d.c-    {
SDL_render_d3d.c-     "direct3d",
SDL_render_d3d.c-     (SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC | SDL_RENDERER_TARGETTEXTURE),
SDL_render_d3d.c-     1,
SDL_render_d3d.c-     {SDL_PIXELFORMAT_ARGB8888},
SDL_render_d3d.c-     0,
SDL_render_d3d.c-     0}
--
SDL_render_d3d11.c:SDL_RenderDriver D3D11_RenderDriver = {
SDL_render_d3d11.c-    D3D11_CreateRenderer,
SDL_render_d3d11.c-    {
SDL_render_d3d11.c-        "direct3d11",
SDL_render_d3d11.c-        (
SDL_render_d3d11.c-            SDL_RENDERER_ACCELERATED |
SDL_render_d3d11.c-            SDL_RENDERER_PRESENTVSYNC |
SDL_render_d3d11.c-            SDL_RENDERER_TARGETTEXTURE
SDL_render_d3d11.c-        ),                          /* flags.  see SDL_RendererFlags */
SDL_render_d3d11.c-        6,                          /* num_texture_formats */
SDL_render_d3d11.c-        {                           /* texture_formats */
SDL_render_d3d11.c-            SDL_PIXELFORMAT_ARGB8888,
SDL_render_d3d11.c-            SDL_PIXELFORMAT_RGB888,
SDL_render_d3d11.c-            SDL_PIXELFORMAT_YV12,
SDL_render_d3d11.c-            SDL_PIXELFORMAT_IYUV,
SDL_render_d3d11.c-            SDL_PIXELFORMAT_NV12,
SDL_render_d3d11.c-            SDL_PIXELFORMAT_NV21
SDL_render_d3d11.c-        },
SDL_render_d3d11.c-        0,                          /* max_texture_width: will be filled in later */
SDL_render_d3d11.c-        0                           /* max_texture_height: will be filled in later */
SDL_render_d3d11.c-    }
SDL_render_d3d11.c-};
--
SDL_render_metal.m:SDL_RenderDriver METAL_RenderDriver = {
SDL_render_metal.m-    METAL_CreateRenderer,
SDL_render_metal.m-    {
SDL_render_metal.m-        "metal",
SDL_render_metal.m-        (SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC | SDL_RENDERER_TARGETTEXTURE),
SDL_render_metal.m-        6,
SDL_render_metal.m-        {
SDL_render_metal.m-            SDL_PIXELFORMAT_ARGB8888,
SDL_render_metal.m-            SDL_PIXELFORMAT_ABGR8888,
SDL_render_metal.m-            SDL_PIXELFORMAT_YV12,
SDL_render_metal.m-            SDL_PIXELFORMAT_IYUV,
SDL_render_metal.m-            SDL_PIXELFORMAT_NV12,
SDL_render_metal.m-            SDL_PIXELFORMAT_NV21
SDL_render_metal.m-        },
SDL_render_metal.m-    0, 0,
SDL_render_metal.m-    }
SDL_render_metal.m-};
--
SDL_render_gl.c:SDL_RenderDriver GL_RenderDriver = {
SDL_render_gl.c-    GL_CreateRenderer,
SDL_render_gl.c-    {
SDL_render_gl.c-     "opengl",
SDL_render_gl.c-     (SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC | SDL_RENDERER_TARGETTEXTURE),
SDL_render_gl.c-     1,
SDL_render_gl.c-     {SDL_PIXELFORMAT_ARGB8888},
SDL_render_gl.c-     0,
SDL_render_gl.c-     0}
SDL_render_gl.c-};
--
SDL_render_gles.c:SDL_RenderDriver GLES_RenderDriver = {
SDL_render_gles.c-    GLES_CreateRenderer,
SDL_render_gles.c-    {
SDL_render_gles.c-     "opengles",
SDL_render_gles.c-     (SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC),
SDL_render_gles.c-     1,
SDL_render_gles.c-     {SDL_PIXELFORMAT_ABGR8888},
SDL_render_gles.c-     0,
SDL_render_gles.c-     0
SDL_render_gles.c-    }
SDL_render_gles.c-};
--
SDL_render_gles2.c:SDL_RenderDriver GLES2_RenderDriver = {
SDL_render_gles2.c-    GLES2_CreateRenderer,
SDL_render_gles2.c-    {
SDL_render_gles2.c-        "opengles2",
SDL_render_gles2.c-        (SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC | SDL_RENDERER_TARGETTEXTURE),
SDL_render_gles2.c-        4,
SDL_render_gles2.c-        {
SDL_render_gles2.c-        SDL_PIXELFORMAT_ARGB8888,
SDL_render_gles2.c-        SDL_PIXELFORMAT_ABGR8888,
SDL_render_gles2.c-        SDL_PIXELFORMAT_RGB888,
SDL_render_gles2.c-        SDL_PIXELFORMAT_BGR888
SDL_render_gles2.c-        },
SDL_render_gles2.c-        0,
SDL_render_gles2.c-        0
SDL_render_gles2.c-    }
SDL_render_gles2.c-};
--
SDL_render_psp.c:SDL_RenderDriver PSP_RenderDriver = {
SDL_render_psp.c-    .CreateRenderer = PSP_CreateRenderer,
SDL_render_psp.c-    .info = {
SDL_render_psp.c-        .name = "PSP",
SDL_render_psp.c-        .flags = SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC | SDL_RENDERER_TARGETTEXTURE,
SDL_render_psp.c-        .num_texture_formats = 4,
SDL_render_psp.c-        .texture_formats = { [0] = SDL_PIXELFORMAT_BGR565,
SDL_render_psp.c-                                                 [1] = SDL_PIXELFORMAT_ABGR1555,
SDL_render_psp.c-                                                 [2] = SDL_PIXELFORMAT_ABGR4444,
SDL_render_psp.c-                                                 [3] = SDL_PIXELFORMAT_ABGR8888,
SDL_render_psp.c-        },
SDL_render_psp.c-        .max_texture_width = 512,
SDL_render_psp.c-        .max_texture_height = 512,
SDL_render_psp.c-     }
SDL_render_psp.c-};
--
SDL_render_sw.c:SDL_RenderDriver SW_RenderDriver = {
SDL_render_sw.c-    SW_CreateRenderer,
SDL_render_sw.c-    {
SDL_render_sw.c-     "software",
SDL_render_sw.c-     SDL_RENDERER_SOFTWARE | SDL_RENDERER_TARGETTEXTURE,
SDL_render_sw.c-     8,
SDL_render_sw.c-     {
SDL_render_sw.c-      SDL_PIXELFORMAT_ARGB8888,
SDL_render_sw.c-      SDL_PIXELFORMAT_ABGR8888,
SDL_render_sw.c-      SDL_PIXELFORMAT_RGBA8888,
SDL_render_sw.c-      SDL_PIXELFORMAT_BGRA8888,
SDL_render_sw.c-      SDL_PIXELFORMAT_RGB888,
SDL_render_sw.c-      SDL_PIXELFORMAT_BGR888,
SDL_render_sw.c-      SDL_PIXELFORMAT_RGB565,
SDL_render_sw.c-      SDL_PIXELFORMAT_RGB555
SDL_render_sw.c-     },
SDL_render_sw.c-     0,
SDL_render_sw.c-     0}
SDL_render_sw.c-};
--
SDL_DirectFB_render.c:SDL_RenderDriver DirectFB_RenderDriver = {
SDL_DirectFB_render.c-    DirectFB_CreateRenderer,
SDL_DirectFB_render.c-    {
SDL_DirectFB_render.c-     "directfb",
SDL_DirectFB_render.c-     (SDL_RENDERER_PRESENTVSYNC | SDL_RENDERER_ACCELERATED),
SDL_DirectFB_render.c-     /* (SDL_TEXTUREMODULATE_NONE | SDL_TEXTUREMODULATE_COLOR |
SDL_DirectFB_render.c-      SDL_TEXTUREMODULATE_ALPHA),
SDL_DirectFB_render.c-      (SDL_BLENDMODE_NONE | SDL_BLENDMODE_MASK | SDL_BLENDMODE_BLEND |
SDL_DirectFB_render.c-      SDL_BLENDMODE_ADD | SDL_BLENDMODE_MOD),
SDL_DirectFB_render.c-     (SDL_SCALEMODE_NONE | SDL_SCALEMODE_FAST |
SDL_DirectFB_render.c-      SDL_SCALEMODE_SLOW | SDL_SCALEMODE_BEST), */
SDL_DirectFB_render.c-     0,
SDL_DirectFB_render.c-     {
SDL_DirectFB_render.c-             /* formats filled in later */
SDL_DirectFB_render.c-     },
SDL_DirectFB_render.c-     0,
SDL_DirectFB_render.c-     0}
SDL_DirectFB_render.c-};