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define_calctarget(3) Arcan Lua API define_calctarget(3) NAME define_calctarget - Create a rendertarget with a periodic readback into a Lua callback SYNOPSIS nil define_calctarget( dest_buffer, vid_table, detach, scale, samplerate, call- back ) DESCRIPTION This function inherits some of its behavior from define_rendertarget . Please refer to the description of that function for assistance with the detach , scale and samplerate functions. The callback will follow the prototype function(image, width, height) where image is a table with the following functions: get (x, y, [nchannels=1]) => r, [g, b, a] histogram_impose (destination, *int:mode*, *bool:norm*, *int:dst_row*) frequency (bin, *int:mode*, *bool:normalize*) => r,g,b,a The get function can be used to sample the value at the specified coordi- nates (x,y) that must be 0 <= x < width, 0 <= y < height. Other values will result in a terminal state transition. For the nchannels argument, the permitted values 1,3,4 and will determine the number of returned channels. The histogram_impose function will generate a histogram and store in the first row (or, if provided, dst_row ) of destination , which subsequently must have at least a width of 256 pixels and at least dst_row number of rows, 0-indexed. The frequency function will return the number of occurences from a spe- cific histogram bin and bin should be 0 <= n < 256. The optional normalize argument, default to true, will normalize against the max- bin value per channel. For both histogram_impose and frequency the possible mode values are HISTOGRAM_SPLIT (treat R, G, B, A channels as separate), HISTOGRAM_MERGE (treat R, G, B, A as packed and merge into one bin) or HIS- TOGRAM_MERGE_NOALPHA (treat R, G, B as packed and ignore A) NOTES 1 The callback will be executed as part of the main loop and it is paramount that the processing done is kept to a minimum. 2 When the samplerate is set to 0 for a calctarget, both rendertarget_forceupdate and stepframe target need to be called in order to update the contents and issue a readback. EXAMPLE function cbfun(source, w, h) print(srcary:get(0, 0)); end function define_calctarget0() dstvid = fill_surface(64, 64, 0, 0, 0, 64, 64); srcvid = color_surface(64, 64, 255, 128, 64); define_calctarget(dstvid, {srcvid}, RENDERTARGET_DETACH, RENDERTARGET_SCALE, 10, cbfun); show_image(srcvid); show_image(dstvid); end MISUSE function cbfun(source, w, h) print(srcary:get(0, 0)); end function define_calctarget0() dstvid = fill_surface(64, 64, 0, 0, 0, 64, 64); srcvid = color_surface(64, 64, 255, 128, 64); define_calctarget(WORLDID, {srcvid}, RENDERTARGET_DETACH, RENDERTARGET_SCALE, 10, cbfun); end MISUSE function cbfun(source, w, h) print(srcary:get(0, 0)); end function define_calctarget1() dstvid = fill_surface(64, 64, 0, 0, 0, 64, 64); srcvid = color_surface(64, 64, 255, 128, 64); define_calctarget(dstvid, {srcvid, WORLDID}, RENDERTARGET_DETACH, RENDERTARGET_SCALE, 10, cbfun); end MISUSE function cbfun(source, w, h) print(srcary:get(0, 0)); end function define_calctarget2() dstvid = fill_surface(64, 64, 0, 0, 0, 64, 64); srcvid = color_surface(64, 64, 255, 128, 64); define_calctarget(dstvid, {srcvid}, RENDERTARGET_DETACH, RENDERTARGET_SCALE, 10, define_calctarget); end SEE ALSO: define_rendertarget(3) define_recordtarget(3) fill_surface(3) targetcontrol August 2026 define_calctarget(3)
NAME | SYNOPSIS | DESCRIPTION | NOTES | EXAMPLE | MISUSE | MISUSE | MISUSE | SEE ALSO:
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