###### (This is the legacy documentation for SDL2, the previous stable version; [SDL3](https://wiki.libsdl.org/SDL3/) is the current stable version.) # SDL_ComposeCustomBlendMode Compose a custom blend mode for renderers. ## Header File Defined in [SDL_blendmode.h](https://github.com/libsdl-org/SDL/blob/SDL2/include/SDL_blendmode.h) ## Syntax ```c SDL_BlendMode SDL_ComposeCustomBlendMode(SDL_BlendFactor srcColorFactor, SDL_BlendFactor dstColorFactor, SDL_BlendOperation colorOperation, SDL_BlendFactor srcAlphaFactor, SDL_BlendFactor dstAlphaFactor, SDL_BlendOperation alphaOperation); ``` ## Function Parameters | | | | | ---------------------------------------- | ------------------ | -------------------------------------------------------------------------------------------------------------------------------------- | | [SDL_BlendFactor](SDL_BlendFactor) | **srcColorFactor** | the [SDL_BlendFactor](SDL_BlendFactor) applied to the red, green, and blue components of the source pixels. | | [SDL_BlendFactor](SDL_BlendFactor) | **dstColorFactor** | the [SDL_BlendFactor](SDL_BlendFactor) applied to the red, green, and blue components of the destination pixels. | | [SDL_BlendOperation](SDL_BlendOperation) | **colorOperation** | the [SDL_BlendOperation](SDL_BlendOperation) used to combine the red, green, and blue components of the source and destination pixels. | | [SDL_BlendFactor](SDL_BlendFactor) | **srcAlphaFactor** | the [SDL_BlendFactor](SDL_BlendFactor) applied to the alpha component of the source pixels. | | [SDL_BlendFactor](SDL_BlendFactor) | **dstAlphaFactor** | the [SDL_BlendFactor](SDL_BlendFactor) applied to the alpha component of the destination pixels. | | [SDL_BlendOperation](SDL_BlendOperation) | **alphaOperation** | the [SDL_BlendOperation](SDL_BlendOperation) used to combine the alpha component of the source and destination pixels. | ## Return Value ([SDL_BlendMode](SDL_BlendMode)) Returns an [SDL_BlendMode](SDL_BlendMode) that represents the chosen factors and operations. ## Remarks The functions [SDL_SetRenderDrawBlendMode](SDL_SetRenderDrawBlendMode) and [SDL_SetTextureBlendMode](SDL_SetTextureBlendMode) accept the [SDL_BlendMode](SDL_BlendMode) returned by this function if the renderer supports it. A blend mode controls how the pixels from a drawing operation (source) get combined with the pixels from the render target (destination). First, the components of the source and destination pixels get multiplied with their blend factors. Then, the blend operation takes the two products and calculates the result that will get stored in the render target. Expressed in pseudocode, it would look like this: ```c dstRGB = colorOperation(srcRGB * srcColorFactor, dstRGB * dstColorFactor); dstA = alphaOperation(srcA * srcAlphaFactor, dstA * dstAlphaFactor); ``` Where the functions `colorOperation(src, dst)` and `alphaOperation(src, dst)` can return one of the following: - `src + dst` - `src - dst` - `dst - src` - `min(src, dst)` - `max(src, dst)` The red, green, and blue components are always multiplied with the first, second, and third components of the [SDL_BlendFactor](SDL_BlendFactor), respectively. The fourth component is not used. The alpha component is always multiplied with the fourth component of the [SDL_BlendFactor](SDL_BlendFactor). The other components are not used in the alpha calculation. Support for these blend modes varies for each renderer. To check if a specific [SDL_BlendMode](SDL_BlendMode) is supported, create a renderer and pass it to either [SDL_SetRenderDrawBlendMode](SDL_SetRenderDrawBlendMode) or [SDL_SetTextureBlendMode](SDL_SetTextureBlendMode). They will return with an error if the blend mode is not supported. This list describes the support of custom blend modes for each renderer in SDL 2.0.6. All renderers support the four blend modes listed in the [SDL_BlendMode](SDL_BlendMode) enumeration. - **direct3d**: Supports all operations with all factors. However, some factors produce unexpected results with [`SDL_BLENDOPERATION_MINIMUM`](SDL_BLENDOPERATION_MINIMUM) and [`SDL_BLENDOPERATION_MAXIMUM`](SDL_BLENDOPERATION_MAXIMUM). - **direct3d11**: Same as Direct3D 9. - **opengl**: Supports the [`SDL_BLENDOPERATION_ADD`](SDL_BLENDOPERATION_ADD) operation with all factors. OpenGL versions 1.1, 1.2, and 1.3 do not work correctly with SDL 2.0.6. - **opengles**: Supports the [`SDL_BLENDOPERATION_ADD`](SDL_BLENDOPERATION_ADD) operation with all factors. Color and alpha factors need to be the same. OpenGL ES 1 implementation specific: May also support [`SDL_BLENDOPERATION_SUBTRACT`](SDL_BLENDOPERATION_SUBTRACT) and [`SDL_BLENDOPERATION_REV_SUBTRACT`](SDL_BLENDOPERATION_REV_SUBTRACT). May support color and alpha operations being different from each other. May support color and alpha factors being different from each other. - **opengles2**: Supports the [`SDL_BLENDOPERATION_ADD`](SDL_BLENDOPERATION_ADD), [`SDL_BLENDOPERATION_SUBTRACT`](SDL_BLENDOPERATION_SUBTRACT), [`SDL_BLENDOPERATION_REV_SUBTRACT`](SDL_BLENDOPERATION_REV_SUBTRACT) operations with all factors. - **psp**: No custom blend mode support. - **software**: No custom blend mode support. Some renderers do not provide an alpha component for the default render target. The [`SDL_BLENDFACTOR_DST_ALPHA`](SDL_BLENDFACTOR_DST_ALPHA) and [`SDL_BLENDFACTOR_ONE_MINUS_DST_ALPHA`](SDL_BLENDFACTOR_ONE_MINUS_DST_ALPHA) factors do not have an effect in this case. ## Version This function is available since SDL 2.0.6. ## See Also - [SDL_SetRenderDrawBlendMode](SDL_SetRenderDrawBlendMode) - [SDL_GetRenderDrawBlendMode](SDL_GetRenderDrawBlendMode) - [SDL_SetTextureBlendMode](SDL_SetTextureBlendMode) - [SDL_GetTextureBlendMode](SDL_GetTextureBlendMode) ---- [CategoryAPI](CategoryAPI), [CategoryAPIFunction](CategoryAPIFunction), [CategoryBlendmode](CategoryBlendmode)