Function sdl2_sys::SDL_ComposeCustomBlendMode

source · 
pub unsafe extern "C" fn SDL_ComposeCustomBlendMode(
    srcColorFactor: SDL_BlendFactor,
    dstColorFactor: SDL_BlendFactor,
    colorOperation: SDL_BlendOperation,
    srcAlphaFactor: SDL_BlendFactor,
    dstAlphaFactor: SDL_BlendFactor,
    alphaOperation: SDL_BlendOperation
) -> SDL_BlendMode
Expand description

Compose a custom blend mode for renderers.

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 in SDL 2.0.6. All renderers support the four blend modes listed in the SDL_BlendMode enumeration.

  • direct3d: Supports SDL_BLENDOPERATION_ADD with all factors.
  • direct3d11: Supports all operations with all factors. However, some factors produce unexpected results with SDL_BLENDOPERATION_MINIMUM and SDL_BLENDOPERATION_MAXIMUM.
  • opengl: Supports the 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 operation with all factors. Color and alpha factors need to be the same. OpenGL ES 1 implementation specific: May also support SDL_BLENDOPERATION_SUBTRACT and 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_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.

\param srcColorFactor the SDL_BlendFactor applied to the red, green, and blue components of the source pixels \param dstColorFactor the SDL_BlendFactor applied to the red, green, and blue components of the destination pixels \param colorOperation the SDL_BlendOperation used to combine the red, green, and blue components of the source and destination pixels \param srcAlphaFactor the SDL_BlendFactor applied to the alpha component of the source pixels \param dstAlphaFactor the SDL_BlendFactor applied to the alpha component of the destination pixels \param alphaOperation the SDL_BlendOperation used to combine the alpha component of the source and destination pixels \returns an SDL_BlendMode that represents the chosen factors and operations.

\since This function is available since SDL 2.0.6.

\sa SDL_SetRenderDrawBlendMode \sa SDL_GetRenderDrawBlendMode \sa SDL_SetTextureBlendMode \sa SDL_GetTextureBlendMode