Code archives/Graphics/ScaleImageFast

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ScaleImageFast by sswift
(Posted 22 years ago)
This function scales an image an arbitrary amount on each axis, and is 80x faster than the default ScaleImage function in Blitz!

Actually, I should say, it is 80x faster than the ScaleImage function in BlitzPlus. I have not tested it against the ScaleImage function in Blitz3D.

It will probably be faster than the one in Blitz3D as well, but the major speed boost here may be due to CopyRect being hardware accelerated in BlitzPlus. 
; -------------------------------------------------------------------------------------------------------------------------------------
; This function scales an image an arbitrary amount on the X and Y axis, and returns a pointer to the new image.
; The original image is not modified.
;
; This function is 80x faster than the ScaleImage function that comes with Blitz! 
; -------------------------------------------------------------------------------------------------------------------------------------
Function ScaleImageFast(SrcImage, ScaleX#, ScaleY#)

	Local SrcWidth,  SrcHeight
	Local DestWidth, DestHeight
	Local ScratchImage, DestImage
	Local SrcBuffer, ScratchBuffer, DestBuffer
	Local X1, Y1, X2, Y2

	; Get the width and height of the source image. 	
		SrcWidth  = ImageWidth(SrcImage)
		SrcHeight = ImageHeight(SrcImage)

	; Calculate the width and height of the dest image.
		DestWidth  = Floor(SrcWidth  * ScaleX#)
		DestHeight = Floor(SrcHeight * ScaleY#)

	; If the image does not need to be scaled, just copy the image and exit the function.
		If (SrcWidth = DestWidth) And (SrcHeight = DestHeight) Then Return CopyImage(SrcImage)

	; Create a scratch image that is as tall as the source image, and as wide as the destination image.
		ScratchImage = CreateImage(DestWidth, SrcHeight)
				
	; Create the destination image.
		DestImage = CreateImage(DestWidth, DestHeight) 

	; Get pointers to the image buffers.
		SrcBuffer     = ImageBuffer(SrcImage)
		ScratchBuffer = ImageBuffer(ScratchImage)
		DestBuffer    = ImageBuffer(DestImage)

	; Duplicate columns from source image to scratch image.
		For X2 = 0 To DestWidth-1
			X1 = Floor(X2 / ScaleX#)
			CopyRect X1, 0, 1, SrcHeight, X2, 0, SrcBuffer, ScratchBuffer
		Next
			
	; Duplicate rows from scratch image to destination image.
		For Y2 = 0 To DestHeight-1
			Y1 = Floor(Y2 / ScaleY#)
			CopyRect 0, Y1, DestWidth, 1, 0, Y2, ScratchBuffer, DestBuffer
		Next
						
	; Free the scratch image.
		FreeImage ScratchImage					
						
	; Return the new image.
		Return DestImage
					
End Function