BlendMode* {...}{.size: sizeof(cint).} = enum
  BLENDMODE_NONE = 0x00000000, ## no blending
                                ## dstRGBA = srcRGBA
  BLENDMODE_BLEND = 0x00000001, ## alpha blending
                                 ## dstRGB = (srcRGB * srcA) + (dstRGB * (1-srcA))
                                 ## dstA = srcA + (dstA * (1-srcA))
  BLENDMODE_ADD = 0x00000002, ## additive blending
                               ## dstRGB = (srcRGB * srcA) + dstRGB
                               ## dstA = dstA
  BLENDMODE_MOD = 0x00000004, ## color modulate
                               ## dstRGB = srcRGB * dstRGB
                               ## dstA = dstA
  BLENDMODE_MUL = 0x00000008, ## color multiply
                               ## dstRGB = (srcRGB * dstRGB) + (dstRGB * (1-srcA))
                               ## dstA = (srcA * dstA) + (dstA * (1-srcA))
  BLENDMODE_INVALID = 0x7FFFFFFF

BlendOperation* {...}{.size: sizeof(cint).} = enum
  BLENDOPERATION_ADD = 0x00000001, ## dst + src : supported by all renderers
  BLENDOPERATION_SUBTRACT = 0x00000002, ## dst - src : supported by D3D9, D3D11, OpenGL, OpenGLES
  BLENDOPERATION_REV_SUBTRACT = 0x00000003, ## src - dst : supported by D3D9, D3D11, OpenGL, OpenGLES
  BLENDOPERATION_MINIMUM = 0x00000004, ## min(dst, src) : supported by D3D11
  BLENDOPERATION_MAXIMUM = 0x00000005 ## max(dst, src) : supported by D3D11

BlendFactor* {...}{.size: sizeof(cint).} = enum
  BLENDFACTOR_ZERO = 0x00000001, ## 0, 0, 0, 0
  BLENDFACTOR_ONE = 0x00000002, ## 1, 1, 1, 1
  BLENDFACTOR_SRC_COLOR = 0x00000003, ## srcR, srcG, srcB, srcA
  BLENDFACTOR_ONE_MINUS_SRC_COLOR = 0x00000004, ## 1-srcR, 1-srcG, 1-srcB, 1-srcA
  BLENDFACTOR_SRC_ALPHA = 0x00000005, ## srcA, srcA, srcA, srcA
  BLENDFACTOR_ONE_MINUS_SRC_ALPHA = 0x00000006, ## 1-srcA, 1-srcA, 1-srcA, 1-srcA
  BLENDFACTOR_DST_COLOR = 0x00000007, ## dstR, dstG, dstB, dstA
  BLENDFACTOR_ONE_MINUS_DST_COLOR = 0x00000008, ## 1-dstR, 1-dstG, 1-dstB, 1-dstA
  BLENDFACTOR_DST_ALPHA = 0x00000009, ## dstA, dstA, dstA, dstA
  BLENDFACTOR_ONE_MINUS_DST_ALPHA = 0x0000000A ## 1-dstA, 1-dstA, 1-dstA, 1-dstA

proc composeCustomBlendMode*(srcColorFactor: BlendFactor;
                             dstColorFactor: BlendFactor;
                             colorOperation: BlendOperation;
                             srcAlphaFactor: BlendFactor;
                             dstAlphaFactor: BlendFactor;
                             alphaOperation: BlendOperation): BlendMode {...}{.cdecl,
    importc: "SDL_ComposeCustomBlendMode", dynlib: SDL2_LIB.}