by Michael A. Seel (4 Submissions)
Category: Graphics
Compatability: Visual Basic 5.0
Difficulty: Unknown Difficulty
Originally Published: Wed 15th November 2000
Date Added: Mon 8th February 2021
Rating: 
(1 Votes)
Function to perform 24-bit alpha blending between two 24-bit colors. Also provides function using GetPixel and SetPixel API calls to blend
API Declarations
Public Declare Function SetPixel Lib "gdi32" (ByVal hdc As Long, ByVal x As Long, ByVal y As Long, ByVal crColor As Long) As Long
VBcoders
' SrcColor: "Top" Color
' DstColor: "Bottom" Color
' Alpha: Alpha transparency levels (24-bit)
' ** Alpha is used as a long in order to specify Red, Green, and Blue alpha
' ** transparency levels (24-bit). To use a single-byte (8-bit) alpha transparency
' ** level, use the Simplify function to convert.
Dim bSrcR As Byte, bSrcG As Byte, bSrcB As Byte
Dim bDstR As Byte, bDstG As Byte, bDstB As Byte
Dim bAlpR As Byte, bAlpG As Byte, bAlpB As Byte
Dim bResR As Byte, bResG As Byte, bResB As Byte
' Split colors and alpha into RGB components
bSrcR = CByte(SrcColor And 255)
bSrcG = CByte(Int(SrcColor / 256) And 255)
bSrcB = CByte(Int(SrcColor / 65536) And 255)
bDstR = CByte(DstColor And 255)
bDstG = CByte(Int(DstColor / 256) And 255)
bDstB = CByte(Int(DstColor / 65536) And 255)
bAlpR = CByte(Alpha And 255)
bAlpG = CByte(Int(Alpha / 256) And 255)
bAlpB = CByte(Int(Alpha / 65536) And 255)
' Calculate 24-bt alpha values
bResR = CInt(bDstR) + ((CInt(bSrcR) - CInt(bDstR)) * (bAlpR / 255))
bResG = CInt(bDstG) + ((CInt(bSrcG) - CInt(bDstG)) * (bAlpG / 255))
bResB = CInt(bDstB) + ((CInt(bSrcB) - CInt(bDstB)) * (bAlpB / 255))
' Return blended 24-bit color
Blend = RGB(bResR, bResG, bResB)
End Function
Public Function BlendPixels(ByVal SrcDC As Long, ByVal SrcX As Integer, ByVal SrcY As Integer, ByVal DstDC As Long, ByVal DstX As Integer, ByVal DstY As Integer, ByVal Alpha As Long) As Long
' Blends the color pixel SrcX, SrcY from SrcDC with the color of
' pixel DstX, DstY from DstDC and paints it to pixel DstX, DstY of DstDC
' SrcDC: hDC of image to use as source pixel in blend
' DstDC: hDC of image to use as destination in blend and to paint output to
BlendPixels = SetPixel(DstDC, DstX, DstY, Blend(GetPixel(SrcDC, SrcX, SrcY), GetPixel(DstDC, DstX, DstY), Alpha))
End Function
Public Function Simplify(ByVal Alpha As Byte) As Long
' Converts an 8-bit alpha transparency level to 24-bit (RGB) alpha transparency levels
Simplify = RGB(Alpha, Alpha, Alpha)
End Function
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