For an eBook or printed book on using the API with Liberty BASIC, see: APIs for Liberty BASIC
Native Commands for Memory Bmp
The graphics command "GETBMP" captures an image from the graphicbox into memory. It looks like this:
#1.g "getbmp display 0 0 160 190"
We give the captured image a one-word name. In this example, it is "display". We also specify the X location to begin the capture, the Y location to begin the capture, the width to capture and the height to capture.
hBmp()
To use the image captured into memory with Liberty BASIC commands with API calls, we get its handle with hBmp(). We place the bitmap name inside of quotation marks, because it is a string.
handleBmp =hbmp("display")
SelectObject
We can use SelectObject to select the mrmory bitmap created by Liberty BASIC into a memory device context.
CallDLL#gdi32,"SelectObject",_
hMemDC asuLong,_ 'memory DC
handleBmp asuLong,_ 'handle of bmp
oldBmp asuLong'returns previously selected bitmap
StretchBlt
The StretchBlt function copies a bitmap from a source rectangle into a destination rectangle, stretching or compressing the bitmap to fit the dimensions of the destination rectangle, if necessary. The system stretches or compresses the bitmap according to the stretching mode currently set in the destination device context.
The source device context and the destination context can be the same or they can be different. They can be window or memory device contexts.
Syntax of StretchBlt
CallDll#gdi32,"StretchBlt", _
hDestDC asulong,_ 'handle to destination DC
xDest aslong,_ 'ulx location on destination
yDest aslong,_ 'uly location on destination
wSrc aslong,_ 'width to stretch to
hSrc aslong,_ 'height to stretch to
hSrcDC asulong,_ 'handle to source DC
xSrc aslong,_ 'ulx location in source
ySrc aslong,_ 'uly location in source
wSrc aslong,_ 'width to take from source
hSrc aslong,_ 'height to take from source
DWROP asulong,_ 'The operation to be performed
result aslong'nonzero if successful
Flipping and Mirroring
In addition to performing stretching or compressing, StretchBlt also allows a program to flip an image vertically, horizontally or both. By making either the Source Width and Height or the Destination Width and Height (but not both source and destination) a negative value, StretchBlt flips the image on the axis that has the negative value. If both the Source and the destination have a negative value, no flipping occurs. If a negative destination width is used, the image is mirrored side-to-side. If a negative destination height is used, the image is flipped top-to-bottom. If both destination width and height are passed as negative numbers, the effect of a 180 degree rotation is achieved.
Placement for Flipping and Mirroring
The x, y placement for the image is always the starting point for the bit transfer. If a negative destination width is passed into the function, the transfer starts at the coordinates specified, but proceeds in the negative width direction. If the destination x-origin coordinate happens to be 0, the image is not visitble, because it displays off of the left side of the screen. If mirroring the image side-to-side, use a starting coordinate to designate where to place the RIGHT side of the image, rather than the usual LEFT side. The same is true for flipping top-to-bottom. If a negative height is passed into the StretchBlt function, the destination Y coordinate for placement should designate the BOTTOM rather than the usual TOP of the image.
If an image is to be mirrored, the x-origin must designate the desired RIGHT side coordinate to place the image. If the image is to be flipped, the y-origin must designate the desired BOTTOM coordinate to place the image. If it is to be both flipped and mirrored, then both origins must be shifted. Instead of indicating the upper left corner, these coordinates now indicate the lower right corner to position the image.
SetStretchBltMode
The SetStretchBltMode function sets the bitmap stretching mode in the specified device context.
SetStretchBltMode Syntax
calldll#gdi32,"SetStretchBltMode",_
hdc asulong,_ 'destination DC
STRETCHMODE aslong,_ 'mode
result aslong'returns previous mode
Stretching Modes
The possible stretching modes are listed below. Precede the Windows Constant with an underscore to alert Liberty BASIC to use the proper value.
BLACKONWHITE
becomes
_BLACKONWHITE
Here is a list of the modes, along with their descriptions.
BLACKONWHITE
Performs a Boolean AND operation using the color values for the eliminated and existing pixels. If the bitmap is a monochrome bitmap, this mode preserves black pixels at the expense of white pixels.
COLORONCOLOR
Deletes the pixels. This mode deletes all eliminated lines of pixels without trying to preserve their information.
HALFTONE
Maps pixels from the source rectangle into blocks of pixels in the destination rectangle. The average color over the destination block of pixels approximates the color of the source pixels. After setting the HALFTONE stretching mode, an application must call the SetBrushOrgEx function to set the brush origin. If it fails to do so, brush misalignment occurs.
WHITEONBLACK
Performs a Boolean OR operation using the color values for the eliminated and existing pixels. If the bitmap is a monochrome bitmap, this mode preserves white pixels at the expense of black pixels.
The stretching mode defines how the system combines rows or columns of a bitmap with existing pixels on a display device when an application calls the StretchBlt function.
The BLACKONWHITE and WHITEONBLACK modes are typically used to preserve foreground pixels in monochrome bitmaps. The COLORONCOLOR mode is typically used to preserve color in color bitmaps.
The HALFTONE mode is slower and requires more processing of the source image than the other three modes; but produces higher quality images. Also note that SetBrushOrgEx must be called after setting the HALFTONE mode to avoid brush misalignment.
Stretch Demo
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 pink; backcolor blue; 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")
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 bitmapcalldll#gdi32,"SetStretchBltMode",_
hdc asulong,_ 'destination DC
_COLORONCOLOR aslong,_ 'mode
result aslong'returns previous mode'capture image and place a resized copy next to the originalCallDll#gdi32,"StretchBlt", _
hdc asulong,_ 'The destination DC = graphicbox200aslong,_ 'x location on destination0aslong,_ 'y location on destination480aslong,_ '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
_SRCCOPY asulong,_'The operation to be performed
result aslong'nonzero if successfulwait[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
Mirror-Stretch Demo
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 pink; backcolor blue; 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")
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 bitmapcalldll#gdi32,"SetStretchBltMode",_
hdc asulong,_ 'destination DC
_COLORONCOLOR aslong,_ 'mode
result aslong'returns previous mode'capture image and place a resized, mirror copy next to the original'with negative width, x location is right X, rather than left X locationCallDll#gdi32,"StretchBlt", _
hdc asulong,_ 'The destination DC = graphicbox480aslong,_ 'x location on destination0aslong,_ 'y location on destination-250aslong,_ '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
_SRCCOPY asulong,_'The operation to be performed
result aslong'nonzero if successfulwait[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
-
Native Commands for Memory Bmp | hBmp() | SelectObject | StretchBlt | Syntax of StretchBlt | Flipping and Mirroring | Placement for Flipping and Mirroring | SetStretchBltMode | SetStretchBltMode Syntax | Stretching Modes | Stretch Demo | Mirror-Stretch Demo 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
Native Commands for Memory Bmp
The graphics command "GETBMP" captures an image from the graphicbox into memory. It looks like this:
We give the captured image a one-word name. In this example, it is "display". We also specify the X location to begin the capture, the Y location to begin the capture, the width to capture and the height to capture.
hBmp()
To use the image captured into memory with Liberty BASIC commands with API calls, we get its handle with hBmp(). We place the bitmap name inside of quotation marks, because it is a string.
SelectObject
We can use SelectObject to select the mrmory bitmap created by Liberty BASIC into a memory device context.
StretchBlt
The StretchBlt function copies a bitmap from a source rectangle into a destination rectangle, stretching or compressing the bitmap to fit the dimensions of the destination rectangle, if necessary. The system stretches or compresses the bitmap according to the stretching mode currently set in the destination device context.The source device context and the destination context can be the same or they can be different. They can be window or memory device contexts.
Syntax of StretchBlt
Flipping and Mirroring
In addition to performing stretching or compressing, StretchBlt also allows a program to flip an image vertically, horizontally or both. By making either the Source Width and Height or the Destination Width and Height (but not both source and destination) a negative value, StretchBlt flips the image on the axis that has the negative value. If both the Source and the destination have a negative value, no flipping occurs. If a negative destination width is used, the image is mirrored side-to-side. If a negative destination height is used, the image is flipped top-to-bottom. If both destination width and height are passed as negative numbers, the effect of a 180 degree rotation is achieved.
Placement for Flipping and Mirroring
The x, y placement for the image is always the starting point for the bit transfer. If a negative destination width is passed into the function, the transfer starts at the coordinates specified, but proceeds in the negative width direction. If the destination x-origin coordinate happens to be 0, the image is not visitble, because it displays off of the left side of the screen. If mirroring the image side-to-side, use a starting coordinate to designate where to place the RIGHT side of the image, rather than the usual LEFT side. The same is true for flipping top-to-bottom. If a negative height is passed into the StretchBlt function, the destination Y coordinate for placement should designate the BOTTOM rather than the usual TOP of the image.
If an image is to be mirrored, the x-origin must designate the desired RIGHT side coordinate to place the image. If the image is to be flipped, the y-origin must designate the desired BOTTOM coordinate to place the image. If it is to be both flipped and mirrored, then both origins must be shifted. Instead of indicating the upper left corner, these coordinates now indicate the lower right corner to position the image.
SetStretchBltMode
The SetStretchBltMode function sets the bitmap stretching mode in the specified device context.
SetStretchBltMode Syntax
Stretching Modes
The possible stretching modes are listed below. Precede the Windows Constant with an underscore to alert Liberty BASIC to use the proper value.
becomes
Here is a list of the modes, along with their descriptions.
The stretching mode defines how the system combines rows or columns of a bitmap with existing pixels on a display device when an application calls the StretchBlt function.
The BLACKONWHITE and WHITEONBLACK modes are typically used to preserve foreground pixels in monochrome bitmaps. The COLORONCOLOR mode is typically used to preserve color in color bitmaps.
The HALFTONE mode is slower and requires more processing of the source image than the other three modes; but produces higher quality images. Also note that SetBrushOrgEx must be called after setting the HALFTONE mode to avoid brush misalignment.
Stretch Demo
Mirror-Stretch Demo
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