(This is the documentation for SDL3, which is the current stable version. SDL2 was the previous version!)

SDL_ComposeCustomBlendMode

Compose a custom blend mode for renderers.

Header File

Syntax

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	srcColorFactor	the SDL_BlendFactor applied to the red, green, and blue components of the source pixels.
SDL_BlendFactor	dstColorFactor	the SDL_BlendFactor applied to the red, green, and blue components of the destination pixels.
SDL_BlendOperation	colorOperation	the SDL_BlendOperation used to combine the red, green, and blue components of the source and destination pixels.
SDL_BlendFactor	srcAlphaFactor	the SDL_BlendFactor applied to the alpha component of the source pixels.
SDL_BlendFactor	dstAlphaFactor	the SDL_BlendFactor applied to the alpha component of the destination pixels.
SDL_BlendOperation	alphaOperation	the SDL_BlendOperation used to combine the alpha component of the source and destination pixels.

Return Value

(SDL_BlendMode) Returns an SDL_BlendMode that represents the chosen factors and operations.

Remarks

The functions SDL_SetRenderDrawBlendMode and SDL_SetTextureBlendMode accept the 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:

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, respectively. The fourth component is not used.

The alpha component is always multiplied with the fourth component of the 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 is supported, create a renderer and pass it to either SDL_SetRenderDrawBlendMode or 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. All renderers support the four blend modes listed in the SDL_BlendMode enumeration.

direct3d: Supports all operations with all factors. However, some factors produce unexpected results with SDL_BLENDOPERATION_MINIMUM and SDL_BLENDOPERATION_MAXIMUM.
direct3d11: Same as Direct3D 9.
opengl: Supports the SDL_BLENDOPERATION_ADD operation with all factors. OpenGL versions 1.1, 1.2, and 1.3 do not work correctly here.
opengles2: Supports the SDL_BLENDOPERATION_ADD, SDL_BLENDOPERATION_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 and SDL_BLENDFACTOR_ONE_MINUS_DST_ALPHA factors do not have an effect in this case.

Thread Safety

It is safe to call this function from any thread.

Version

This function is available since SDL 3.1.3.