For an eBook or printed book on using the API with Liberty BASIC, see: APIs for Liberty BASIC
TransparentBlt
The TransparentBlt function performs a bit-block transfer of the color data corresponding to a rectangle of pixels from the specified source device context into a destination device context. Like StretchBlt, it can perform a stretching or shrinking of the image. In addition, it makes transparent the color specified. This allows us to place an image directly on any background without a surrounding rectangle, much like sprites.
There is one other important difference between StretchBlt and TransparentBlt. StretchBlt is part of the Windows DLL GDI32.DLL. This DLL needn't be opened in Liberty BASIC. It can be addressed directly as #gdi32. The TransparentBlt function is part of MSIMG32.DLL. We must open this DLL in order to use it.
open msimg32.dllfordllas#msimg
We must close it when we no longer need it.
close#msimg
Syntax
open"Msimg32.dll"forDLLas#msimg
CallDll#msimg,"TransparentBlt",_
hdc asulong,_ 'The destination DC = graphicbox
xDest aslong,_ 'x location on destination
yDest aslong,_ 'y location on destination
wDest aslong,_ 'width to stretch to
hDest aslong,_ 'height to stretch to
hMemDC asulong,_ 'The source DC = memory
xSrc aslong,_ 'x location in source
ySrc aslong,_ 'y location in source
wSrc aslong,_ 'width to take from source
hSrc aslong,_ 'height to take from source
lColor asulong,_ 'RGB/long color value to make transparent
result asboolean'nonzero if successfulclose#msimg
Remarks
From MSDN: If the source and destination rectangles are not the same size, the source bitmap is stretched to match the destination rectangle. When the SetStretchBltMode function is used, the iStretchMode modes of BLACKONWHITE and WHITEONBLACK are converted to COLORONCOLOR for the TransparentBlt function.
The destination device context specifies the transformation type for the destination coordinates. The source device context specifies the transformation type for the source coordinates.
TransparentBlt does not mirror a bitmap if either the width or height, of either the source or destination, is negative.
The Long Color Value
TransparentBlt allows us to specify the color that is to be transparent when the image is transferred. This needs to be in the form of a single, long value. We get this value from the red, green and blue components with the following formula:
LongColor = (blue*256*256) + (green*256) + red
If the blue value is 200, green is 100 and red is 10, it looks like this:
LongColor = (200*256*256) + (100*256) + 10
Demo One
The following program demonstrates the transparency of the image when it is transferred. The graphicbox is filled with black and a word is printed on it. The code captures a bitmap from the graphicbox, then fills it with yellow. When the original image is transferred back to the graphicbox, the black is transparent, so the word appears properly on the yellow color.
nomainwin
winWide=700:winHigh=500WindowWidth=winWide+50:WindowHeight=winHigh+50UpperLeftX=1:UpperLeftY=1graphicbox#1.g,0,0,winWide,winHigh
open"GDI Demo"forwindowas#1#1"trapclose [quit]"#1.g "down; fill black; backcolor black; color red"#1.g "font arial 20"#1.g "\\\Sample"'capture a bitmap in memory with native commands#1.g "getbmp display 0 0 160 190"'get handle for memory bmp
handleBmp =hbmp("display")#1.g "fill yellow;flush"
h=hwnd(#1.g)'graphicbox handle'get device context for window:calldll#user32,"GetDC",_
h asulong,_ 'graphicbox handle
hdc asulong'returns handle to device contextcalldll#gdi32,"CreateCompatibleDC",_
hdc asulong,_ 'graphicbox DC
hMemDC asulong'memory DCCallDLL#gdi32,"SelectObject",_
hMemDC asuLong,_ 'memory DC
handleBmp asuLong,_ 'handle of bmp
oldBmp asuLong'returns previously selected bitmapopen"Msimg32.dll"forDLLas#msimg
CallDll#msimg,"TransparentBlt",_
hdc asulong,_ 'The destination DC = graphicbox30aslong,_ 'x location on destination0aslong,_ 'y location on destination250aslong,_ 'width to stretch to300aslong,_ 'height to stretch to
hMemDC asulong,_ 'The source DC = memory0aslong,_ 'x location in source0aslong,_ 'y location in source100aslong,_ 'width to take from source90aslong,_ 'height to take from source0asulong,_ 'RGB/long color value to make transparent
result asboolean'nonzero if successfulclose#msimg
wait[quit]calldll#gdi32,"DeleteDC",_
hMemDC asulong,_ 'DC to delete
re aslong'nonzero=successcalldll#user32,"ReleaseDC",_
h asulong,_ 'window handle
hdc asulong,_ 'device context
ret aslongclose#1:end
Demo Two
The second demo is identical to the first, with one important difference. We fill with an RGB color and specify that color as the transparent color in TransparentBlt.
nomainwin
winWide=700:winHigh=500WindowWidth=winWide+50:WindowHeight=winHigh+50UpperLeftX=1:UpperLeftY=1graphicbox#1.g,0,0,winWide,winHigh
open"GDI Demo"forwindowas#1#1"trapclose [quit]"#1.g "down; fill 10 100 200; backcolor 10 100 200; color red"#1.g "font arial 20"#1.g "\\\Sample"'capture a bitmap in memory with native commands#1.g "getbmp display 0 0 160 190"'get handle for memory bmp
handleBmp =hbmp("display")#1.g "fill yellow;flush"
h=hwnd(#1.g)'graphicbox handle'get device context for window:calldll#user32,"GetDC",_
h asulong,_ 'graphicbox handle
hdc asulong'returns handle to device contextcalldll#gdi32,"CreateCompatibleDC",_
hdc asulong,_ 'graphicbox DC
hMemDC asulong'memory DCCallDLL#gdi32,"SelectObject",_
hMemDC asuLong,_ 'memory DC
handleBmp asuLong,_ 'handle of bmp
oldBmp asuLong'returns previously selected bitmap
lColor =(200*256*256)+(100*256)+10open"Msimg32.dll"forDLLas#msimg
CallDll#msimg,"TransparentBlt",_
hdc asulong,_ 'The destination DC = graphicbox30aslong,_ 'x location on destination0aslong,_ 'y location on destination250aslong,_ 'width to stretch to300aslong,_ 'height to stretch to
hMemDC asulong,_ 'The source DC = memory0aslong,_ 'x location in source0aslong,_ 'y location in source100aslong,_ 'width to take from source90aslong,_ 'height to take from source
lColor asulong,_ 'RGB/long color value to make transparent
result asboolean'nonzero if successfulclose#msimg
wait[quit]calldll#gdi32,"DeleteDC",_
hMemDC asulong,_ 'DC to delete
re aslong'nonzero=successcalldll#user32,"ReleaseDC",_
h asulong,_ 'window handle
hdc asulong,_ 'device context
ret aslongclose#1:end
Alyce
Oct 14, 2011
-
For more details on using TransparentBlt, see Janet Terra's TransparentBlt article.
TransparentBlt | Syntax | Remarks | The Long Color Value | Demo One | Demo Two
Some text below is copied from the Microsoft Developers Network Library.
For an eBook or printed book on using the API with Liberty BASIC, see:
APIs for Liberty BASIC
TransparentBlt
The TransparentBlt function performs a bit-block transfer of the color data corresponding to a rectangle of pixels from the specified source device context into a destination device context. Like StretchBlt, it can perform a stretching or shrinking of the image. In addition, it makes transparent the color specified. This allows us to place an image directly on any background without a surrounding rectangle, much like sprites.There is one other important difference between StretchBlt and TransparentBlt. StretchBlt is part of the Windows DLL GDI32.DLL. This DLL needn't be opened in Liberty BASIC. It can be addressed directly as #gdi32. The TransparentBlt function is part of MSIMG32.DLL. We must open this DLL in order to use it.
We must close it when we no longer need it.
Syntax
Remarks
From MSDN:If the source and destination rectangles are not the same size, the source bitmap is stretched to match the destination rectangle. When the SetStretchBltMode function is used, the iStretchMode modes of BLACKONWHITE and WHITEONBLACK are converted to COLORONCOLOR for the TransparentBlt function.
The destination device context specifies the transformation type for the destination coordinates. The source device context specifies the transformation type for the source coordinates.
TransparentBlt does not mirror a bitmap if either the width or height, of either the source or destination, is negative.
The Long Color Value
TransparentBlt allows us to specify the color that is to be transparent when the image is transferred. This needs to be in the form of a single, long value. We get this value from the red, green and blue components with the following formula:LongColor = (blue*256*256) + (green*256) + red
If the blue value is 200, green is 100 and red is 10, it looks like this:
LongColor = (200*256*256) + (100*256) + 10
Demo One
The following program demonstrates the transparency of the image when it is transferred. The graphicbox is filled with black and a word is printed on it. The code captures a bitmap from the graphicbox, then fills it with yellow. When the original image is transferred back to the graphicbox, the black is transparent, so the word appears properly on the yellow color.Demo Two
The second demo is identical to the first, with one important difference. We fill with an RGB color and specify that color as the transparent color in TransparentBlt.
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