# 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)

