/usr/share/psychtoolbox-3/PsychGLImageProcessing/PsychHelperCreateGenericLuminanceToRGBA8LUT.m is in psychtoolbox-3-common 3.0.11.20131230.dfsg1-1build1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 | function luttex = PsychHelperCreateGenericLuminanceToRGBA8LUT(lut)
% luttex = PsychHelperCreateGenericLuminanceToRGBA8LUT(lut);
%
% Helper function for PsychImaging() - Don't call from usercode!
%
% Used by PsychImaging(....,'EnableGenericHighPrecisionLuminanceOutput', lut);
% Converts a luminance -> RGB8 or RGBA8 LUT as provided in the 3- or 4 rows
% by n columns matrix 'lut' into an equivalent RGBA8 lookup table texture,
% then returns the texture handle to the calling routine.
%
% 'lut' = 3 rows by nslots columns uint8 matrix for LUT's that map the
% input luminance value range [0.0 - 1.0] to the integral 0 - nslots range,
% then lookup the corresponding RGB8 output pixel in the lut. If 'lut' has
% 4 rows, then the 4th row encodes alpha-channel - This is only useful for
% debugging, as teh alpha channel can't be output to the external device.
%
% Implementation details:
%
% The lut texture is built as a 256x256 2D rectangle texture, allowing for
% luts with up to 2^16 luminance slots that work on all supported graphics
% hardware. One could extend the size of the texture to up to 8192x8192 on
% latest hardware, allowing for up to 2^26 bits, but that is likely not
% that useful, given that internal GPU precision is restricted to 23 bits
% (floating point single precision) and there doesn't exist a single output
% device with more than 16 bits of output resolution anyway.
%
% We assume GL is available:
global GL;
if nargin < 1
error('Called without mandatory "lut" input argument!');
end
if isempty(lut)
error('Called without mandatory "lut" input argument!');
end
[channels, nslots] = size(lut);
if channels<3 || channels>4
error('lut must have 3 or 4 rows aka channels!');
end
if nslots < 1 || nslots > 2^16
error('lut must have between 1 and 65536 slots, aka columns!');
end
if ~isa(lut,'uint8')
error('lut must by of uint8 type!');
end
% Pad lut with a fourth row of zeros, if it isn't already a 4 row lut:
if channels~=4
lut = [lut ; uint8(zeros(1, nslots))];
end
nrows = ceil(nslots / 256);
ncols = 256;
% Padding required? Expand lut with 'nexpand' zero-slots aka columns if lut
% size is not a multiple of 'ncols' slots:
if mod(nslots, ncols)~=0
nexpand = ncols - mod(nslots, ncols);
lut = [lut , uint8(zeros(4, nexpand))];
end
% Ok, our 'lut' is 4 rows aka channels, and has a multiple of 'ncols' slots
% to cleanly fill 'nrows' rows of a 'nrows' by 'ncols' matrix. Copy it into
% matrix:
clut = uint8(zeros(4, ncols, nrows));
for i=1:nrows
clut(1,:,i) = lut(1, (((i-1)*ncols + 1):(i*ncols)));
clut(2,:,i) = lut(2, (((i-1)*ncols + 1):(i*ncols)));
clut(3,:,i) = lut(3, (((i-1)*ncols + 1):(i*ncols)));
clut(4,:,i) = lut(4, (((i-1)*ncols + 1):(i*ncols)));
end
% Build texture:
% Create and setup texture from 'clut':
luttex = glGenTextures(1);
glBindTexture(GL.TEXTURE_RECTANGLE_EXT, luttex);
glTexImage2D(GL.TEXTURE_RECTANGLE_EXT, 0, GL.RGBA, ncols, nrows, 0, GL.RGBA, GL.UNSIGNED_BYTE, clut);
% Make sure we use nearest neighbour sampling:
glTexParameteri(GL.TEXTURE_RECTANGLE_EXT, GL.TEXTURE_MIN_FILTER, GL.NEAREST);
glTexParameteri(GL.TEXTURE_RECTANGLE_EXT, GL.TEXTURE_MAG_FILTER, GL.NEAREST);
% And that we clamp to edge:
glTexParameteri(GL.TEXTURE_RECTANGLE_EXT, GL.TEXTURE_WRAP_S, GL.CLAMP);
glTexParameteri(GL.TEXTURE_RECTANGLE_EXT, GL.TEXTURE_WRAP_T, GL.CLAMP);
glBindTexture(GL.TEXTURE_RECTANGLE_EXT, 0);
% Ready, return luttex:
return;
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