add support for copy-screen-to-bitmap #153
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adds support for Acorn GXR style “copy screen to bitmap” command sequence this is supported on both `VDU 23,27,1,n,0,0,0` to define bitmap `n` from the last two graphics cursor positions, using an 8-bit bitmap ID and also `VDU 23,27,&21,n;0;` using a 16-bit bitmap/buffer ID these commands are compatible with the existing `VDU 23,27,1` and `VDU 23,27,&21` commands - the system can tell the difference as these variants require a zero “height” value if the buffer specified already exists then it will be deleted/cleared before the new bitmap is created from the screen. the resultant bitmap data will be in vdp-gl’s `Bitmap::Native` format the original Acorn command documentation specifies that a few more zeros should be sent. you can safely send additional zeros, as per Acorn’s documentation, as they will just be ignored. it should be noted that `VDU 23,27,&21` when pointing to an existing buffer to set it to be a bitmap also usually expects a `format` byte, but this isn’t required/supported/needed for copying screen to bitmap, i.e. this command variant requires one less byte to be sent requires an updated/custom vdp-gl
fixes issue with capturing bitmap to buffer zero (the `createBuffer` call was preventing creation of buffer with ID 0, as it can’t be used as a place to redirect output)
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adds support for Acorn GXR style “copy screen to bitmap” command sequence
this is supported on both
VDU 23,27,1,n,0,0,0to define bitmapnfrom the last two graphics cursor positions, using an 8-bit bitmap ID and alsoVDU 23,27,&21,n;0;using a 16-bit bitmap/buffer IDthese commands are compatible with the existing
VDU 23,27,1andVDU 23,27,&21commands - the system can tell the difference as these variants require a zero “height” valueif the buffer specified already exists then it will be deleted/cleared before the new bitmap is created from the screen. the resultant bitmap data will be in vdp-gl’s
Bitmap::Nativeformatthe original Acorn command documentation specifies that a few more zeros should be sent. you can safely send additional zeros, as per Acorn’s documentation, as they will just be ignored.
it should be noted that
VDU 23,27,&21when pointing to an existing buffer to set it to be a bitmap also usually expects aformatbyte, but this isn’t required/supported/needed for copying screen to bitmap, i.e. this command variant requires one less byte to be sentrequires an updated/custom vdp-gl, and can thus currently only be built using PlatformIO