Implemented more flexible blending modes for accelerated renderers

This fixes bug 2594 - Propose new blend mode, SDL_BLENDMODE_BLEND_DSTA

	blendMode = SDL_ComposeCustomBlendMode(SDL_BLENDFACTOR_SRC_ALPHA,
	                                       SDL_BLENDFACTOR_ONE_MINUS_SRC_ALPHA,
	                                       SDL_BLENDOPERATION_ADD,
	                                       SDL_BLENDFACTOR_ZERO,
	                                       SDL_BLENDFACTOR_ONE,
	                                       SDL_BLENDOPERATION_ADD);

This fixes bug 2828 - Subtractive Blending

	blendMode = SDL_ComposeCustomBlendMode(SDL_BLENDFACTOR_SRC_ALPHA,
	                                       SDL_BLENDFACTOR_ONE,
	                                       SDL_BLENDOPERATION_SUBTRACT,
	                                       SDL_BLENDFACTOR_ZERO,
	                                       SDL_BLENDFACTOR_ONE,
	                                       SDL_BLENDOPERATION_SUBTRACT);


This goes partway to fixing bug 3684 - Add support for a pre-multiplied alpha blending mode

	blendMode = SDL_ComposeCustomBlendMode(SDL_BLENDFACTOR_ONE,
	                                       SDL_BLENDFACTOR_ONE_MINUS_SRC_ALPHA,
	                                       SDL_BLENDOPERATION_ADD,
	                                       SDL_BLENDFACTOR_ONE,
	                                       SDL_BLENDFACTOR_ONE_MINUS_SRC_ALPHA,
	                                       SDL_BLENDOPERATION_ADD);

include/SDL_blendmode.h

@@ -47,11 +47,68 @@ typedef enum
     SDL_BLENDMODE_ADD = 0x00000002,      /**< additive blending
                                               dstRGB = (srcRGB * srcA) + dstRGB
                                               dstA = dstA */
-    SDL_BLENDMODE_MOD = 0x00000004       /**< color modulate
+    SDL_BLENDMODE_MOD = 0x00000004,      /**< color modulate
                                               dstRGB = srcRGB * dstRGB
                                               dstA = dstA */
+    SDL_BLENDMODE_INVALID = 0x7FFFFFFF
+
+    /* Additional custom blend modes can be returned by SDL_ComposeCustomBlendMode() */
+
 } SDL_BlendMode;
 
+/**
+ *  \brief The blend operation used when combining source and destination pixel components
+ */
+typedef enum
+{
+    SDL_BLENDOPERATION_ADD              = 0x1,  /**< dst + src: supported by all renderers */
+    SDL_BLENDOPERATION_SUBTRACT         = 0x2,  /**< dst - src : supported by D3D9, D3D11, OpenGL, OpenGLES */
+    SDL_BLENDOPERATION_REV_SUBTRACT     = 0x3,  /**< src - dst : supported by D3D9, D3D11, OpenGL, OpenGLES */
+    SDL_BLENDOPERATION_MINIMUM          = 0x4,  /**< min(dst, src) : supported by D3D11 */
+    SDL_BLENDOPERATION_MAXIMUM          = 0x5,  /**< max(dst, src) : supported by D3D11 */
+
+} SDL_BlendOperation;
+
+/**
+ *  \brief The normalized factor used to multiply pixel components
+ */
+typedef enum
+{
+    SDL_BLENDFACTOR_ZERO                = 0x1,  /**< 0, 0, 0, 0 */
+    SDL_BLENDFACTOR_ONE                 = 0x2,  /**< 1, 1, 1, 1 */
+    SDL_BLENDFACTOR_SRC_COLOR           = 0x3,  /**< srcR, srcG, srcB, srcA */
+    SDL_BLENDFACTOR_ONE_MINUS_SRC_COLOR = 0x4,  /**< 1-srcR, 1-srcG, 1-srcB, 1-srcA */
+    SDL_BLENDFACTOR_SRC_ALPHA           = 0x5,  /**< srcA, srcA, srcA, srcA */
+    SDL_BLENDFACTOR_ONE_MINUS_SRC_ALPHA = 0x6,  /**< 1-srcA, 1-srcA, 1-srcA, 1-srcA */
+    SDL_BLENDFACTOR_DST_COLOR           = 0x7,  /**< dstR, dstG, dstB, dstA */
+    SDL_BLENDFACTOR_ONE_MINUS_DST_COLOR = 0x8,  /**< 1-dstR, 1-dstG, 1-dstB, 1-dstA */
+    SDL_BLENDFACTOR_DST_ALPHA           = 0x9,  /**< dstA, dstA, dstA, dstA */
+    SDL_BLENDFACTOR_ONE_MINUS_DST_ALPHA = 0xA,  /**< 1-dstA, 1-dstA, 1-dstA, 1-dstA */
+
+} SDL_BlendFactor;
+
+/**
+ *  \brief Create a custom blend mode, which may or may not be supported by a given renderer
+ *
+ *  \param srcColorFactor
+ *  \param dstColorFactor
+ *  \param colorOperation
+ *  \param srcAlphaFactor
+ *  \param dstAlphaFactor
+ *  \param alphaOperation
+ *
+ *  The result of the blend mode operation will be:
+ *      dstRGB = dstRGB * dstColorFactor colorOperation srcRGB * srcColorFactor
+ *  and
+ *      dstA = dstA * dstAlphaFactor alphaOperation srcA * srcAlphaFactor
+ */
+extern DECLSPEC SDL_BlendMode SDLCALL SDL_ComposeCustomBlendMode(SDL_BlendFactor srcColorFactor,
+                                                                 SDL_BlendFactor dstColorFactor,
+                                                                 SDL_BlendOperation colorOperation,
+                                                                 SDL_BlendFactor srcAlphaFactor,
+                                                                 SDL_BlendFactor dstAlphaFactor,
+                                                                 SDL_BlendOperation alphaOperation);
+
 /* Ends C function definitions when using C++ */
 #ifdef __cplusplus
 }

src/dynapi/SDL_dynapi_overrides.h

@@ -627,3 +627,4 @@
 #define SDL_utf8strlen SDL_utf8strlen_REAL
 #define SDL_LoadFile_RW SDL_LoadFile_RW_REAL
 #define SDL_wcscmp SDL_wcscmp_REAL
+#define SDL_ComposeCustomBlendMode SDL_ComposeCustomBlendMode_REAL

src/dynapi/SDL_dynapi_procs.h

@@ -659,3 +659,4 @@ SDL_DYNAPI_PROC(SDL_JoystickID,SDL_JoystickGetDeviceInstanceID,(int a),(a),retur
 SDL_DYNAPI_PROC(size_t,SDL_utf8strlen,(const char *a),(a),return)
 SDL_DYNAPI_PROC(void*,SDL_LoadFile_RW,(SDL_RWops *a, size_t *b, int c),(a,b,c),return)
 SDL_DYNAPI_PROC(int,SDL_wcscmp,(const wchar_t *a, const wchar_t *b),(a,b),return)
+SDL_DYNAPI_PROC(SDL_BlendMode,SDL_ComposeCustomBlendMode,(SDL_BlendFactor a, SDL_BlendFactor b, SDL_BlendOperation c, SDL_BlendFactor d, SDL_BlendFactor e, SDL_BlendOperation f),(a,b,c,d,e,f),return)

src/render/SDL_render.c

@@ -44,6 +44,31 @@
         return retval; \
     }
 
+/* Predefined blend modes */
+#define SDL_COMPOSE_BLENDMODE(srcColorFactor, dstColorFactor, colorOperation, \
+                              srcAlphaFactor, dstAlphaFactor, alphaOperation) \
+    (SDL_BlendMode)(((Uint32)colorOperation << 0) | \
+                    ((Uint32)srcColorFactor << 4) | \
+                    ((Uint32)dstColorFactor << 8) | \
+                    ((Uint32)alphaOperation << 16) | \
+                    ((Uint32)srcAlphaFactor << 20) | \
+                    ((Uint32)dstAlphaFactor << 24))
+
+#define SDL_BLENDMODE_NONE_FULL \
+    SDL_COMPOSE_BLENDMODE(SDL_BLENDFACTOR_ONE, SDL_BLENDFACTOR_ZERO, SDL_BLENDOPERATION_ADD, \
+                          SDL_BLENDFACTOR_ONE, SDL_BLENDFACTOR_ZERO, SDL_BLENDOPERATION_ADD)
+
+#define SDL_BLENDMODE_BLEND_FULL \
+    SDL_COMPOSE_BLENDMODE(SDL_BLENDFACTOR_SRC_ALPHA, SDL_BLENDFACTOR_ONE_MINUS_SRC_ALPHA, SDL_BLENDOPERATION_ADD, \
+                          SDL_BLENDFACTOR_ONE, SDL_BLENDFACTOR_ONE_MINUS_SRC_ALPHA, SDL_BLENDOPERATION_ADD)
+
+#define SDL_BLENDMODE_ADD_FULL \
+    SDL_COMPOSE_BLENDMODE(SDL_BLENDFACTOR_SRC_ALPHA, SDL_BLENDFACTOR_ONE, SDL_BLENDOPERATION_ADD, \
+                          SDL_BLENDFACTOR_ZERO, SDL_BLENDFACTOR_ONE, SDL_BLENDOPERATION_ADD)
+
+#define SDL_BLENDMODE_MOD_FULL \
+    SDL_COMPOSE_BLENDMODE(SDL_BLENDFACTOR_ZERO, SDL_BLENDFACTOR_SRC_COLOR, SDL_BLENDOPERATION_ADD, \
+                          SDL_BLENDFACTOR_ZERO, SDL_BLENDFACTOR_ONE, SDL_BLENDOPERATION_ADD)
 
 #if !SDL_RENDER_DISABLED
 static const SDL_RenderDriver *render_drivers[] = {
@@ -379,6 +404,23 @@ SDL_GetRendererOutputSize(SDL_Renderer * renderer, int *w, int *h)
     }
 }
 
+static SDL_bool
+IsSupportedBlendMode(SDL_Renderer * renderer, SDL_BlendMode blendMode)
+{
+    switch (blendMode)
+    {
+    /* These are required to be supported by all renderers */
+    case SDL_BLENDMODE_NONE:
+    case SDL_BLENDMODE_BLEND:
+    case SDL_BLENDMODE_ADD:
+    case SDL_BLENDMODE_MOD:
+        return SDL_TRUE;
+
+    default:
+        return renderer->SupportsBlendMode && renderer->SupportsBlendMode(renderer, blendMode);
+    }
+}
+
 static SDL_bool
 IsSupportedFormat(SDL_Renderer * renderer, Uint32 format)
 {
@@ -706,6 +748,9 @@ SDL_SetTextureBlendMode(SDL_Texture * texture, SDL_BlendMode blendMode)
     CHECK_TEXTURE_MAGIC(texture, -1);
 
     renderer = texture->renderer;
+    if (!IsSupportedBlendMode(renderer, blendMode)) {
+        return SDL_Unsupported();
+    }
     texture->blendMode = blendMode;
     if (texture->native) {
         return SDL_SetTextureBlendMode(texture->native, blendMode);
@@ -1452,6 +1497,9 @@ SDL_SetRenderDrawBlendMode(SDL_Renderer * renderer, SDL_BlendMode blendMode)
 {
     CHECK_RENDERER_MAGIC(renderer, -1);
 
+    if (!IsSupportedBlendMode(renderer, blendMode)) {
+        return SDL_Unsupported();
+    }
     renderer->blendMode = blendMode;
     return 0;
 }
@@ -2042,4 +2090,91 @@ int SDL_GL_UnbindTexture(SDL_Texture *texture)
     return SDL_Unsupported();
 }
 
+static SDL_BlendMode
+SDL_GetShortBlendMode(SDL_BlendMode blendMode)
+{
+    switch (blendMode) {
+    case SDL_BLENDMODE_NONE_FULL:
+        return SDL_BLENDMODE_NONE;
+    case SDL_BLENDMODE_BLEND_FULL:
+        return SDL_BLENDMODE_BLEND;
+    case SDL_BLENDMODE_ADD_FULL:
+        return SDL_BLENDMODE_ADD;
+    case SDL_BLENDMODE_MOD_FULL:
+        return SDL_BLENDMODE_MOD;
+    default:
+        return blendMode;
+    }
+}
+
+static SDL_BlendMode
+SDL_GetLongBlendMode(SDL_BlendMode blendMode)
+{
+    switch (blendMode) {
+    case SDL_BLENDMODE_NONE:
+        return SDL_BLENDMODE_NONE_FULL;
+    case SDL_BLENDMODE_BLEND:
+        return SDL_BLENDMODE_BLEND_FULL;
+    case SDL_BLENDMODE_ADD:
+        return SDL_BLENDMODE_ADD_FULL;
+    case SDL_BLENDMODE_MOD:
+        return SDL_BLENDMODE_MOD_FULL;
+    default:
+        return blendMode;
+    }
+}
+
+SDL_BlendMode
+SDL_ComposeCustomBlendMode(SDL_BlendFactor srcColorFactor, SDL_BlendFactor dstColorFactor,
+                           SDL_BlendOperation colorOperation,
+                           SDL_BlendFactor srcAlphaFactor, SDL_BlendFactor dstAlphaFactor,
+                           SDL_BlendOperation alphaOperation)
+{
+    SDL_BlendMode blendMode = SDL_COMPOSE_BLENDMODE(srcColorFactor, dstColorFactor, colorOperation,
+                                                    srcAlphaFactor, dstAlphaFactor, alphaOperation);
+    return SDL_GetShortBlendMode(blendMode);
+}
+
+SDL_BlendFactor
+SDL_GetBlendModeSrcColorFactor(SDL_BlendMode blendMode)
+{
+    blendMode = SDL_GetLongBlendMode(blendMode);
+    return (SDL_BlendFactor)(((Uint32)blendMode >> 4) & 0xF);
+}
+
+SDL_BlendFactor
+SDL_GetBlendModeDstColorFactor(SDL_BlendMode blendMode)
+{
+    blendMode = SDL_GetLongBlendMode(blendMode);
+    return (SDL_BlendFactor)(((Uint32)blendMode >> 8) & 0xF);
+}
+
+SDL_BlendOperation
+SDL_GetBlendModeColorOperation(SDL_BlendMode blendMode)
+{
+    blendMode = SDL_GetLongBlendMode(blendMode);
+    return (SDL_BlendOperation)(((Uint32)blendMode >> 0) & 0xF);
+}
+
+SDL_BlendFactor
+SDL_GetBlendModeSrcAlphaFactor(SDL_BlendMode blendMode)
+{
+    blendMode = SDL_GetLongBlendMode(blendMode);
+    return (SDL_BlendFactor)(((Uint32)blendMode >> 20) & 0xF);
+}
+
+SDL_BlendFactor
+SDL_GetBlendModeDstAlphaFactor(SDL_BlendMode blendMode)
+{
+    blendMode = SDL_GetLongBlendMode(blendMode);
+    return (SDL_BlendFactor)(((Uint32)blendMode >> 24) & 0xF);
+}
+
+SDL_BlendOperation
+SDL_GetBlendModeAlphaOperation(SDL_BlendMode blendMode)
+{
+    blendMode = SDL_GetLongBlendMode(blendMode);
+    return (SDL_BlendFactor)(((Uint32)blendMode >> 16) & 0xF);
+}
+
 /* vi: set ts=4 sw=4 expandtab: */

src/render/SDL_sysrender.h

@@ -79,6 +79,7 @@ struct SDL_Renderer
 
     void (*WindowEvent) (SDL_Renderer * renderer, const SDL_WindowEvent *event);
     int (*GetOutputSize) (SDL_Renderer * renderer, int *w, int *h);
+    SDL_bool (*SupportsBlendMode)(SDL_Renderer * renderer, SDL_BlendMode blendMode);
     int (*CreateTexture) (SDL_Renderer * renderer, SDL_Texture * texture);
     int (*SetTextureColorMod) (SDL_Renderer * renderer,
                                SDL_Texture * texture);
@@ -186,6 +187,14 @@ extern SDL_RenderDriver DirectFB_RenderDriver;
 extern SDL_RenderDriver PSP_RenderDriver;
 extern SDL_RenderDriver SW_RenderDriver;
 
+/* Blend mode functions */
+extern SDL_BlendFactor SDL_GetBlendModeSrcColorFactor(SDL_BlendMode blendMode);
+extern SDL_BlendFactor SDL_GetBlendModeDstColorFactor(SDL_BlendMode blendMode);
+extern SDL_BlendOperation SDL_GetBlendModeColorOperation(SDL_BlendMode blendMode);
+extern SDL_BlendFactor SDL_GetBlendModeSrcAlphaFactor(SDL_BlendMode blendMode);
+extern SDL_BlendFactor SDL_GetBlendModeDstAlphaFactor(SDL_BlendMode blendMode);
+extern SDL_BlendOperation SDL_GetBlendModeAlphaOperation(SDL_BlendMode blendMode);
+
 #endif /* SDL_sysrender_h_ */
 
 /* vi: set ts=4 sw=4 expandtab: */