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/* SubpixelDrive_FormattingShader -- Subpixel drive output formatter
*
* This shader packs 3 horizontally adjacent 8 bpc luminance pixels
* into one output pixel, packing the three 8 bpc luminance values
* into the three color channels of the output pixel. A monitor with
* subpixel drive will decode this info again to drive 3 luminance
* subpixels per output pixel, for three times the horizontal resolution.
*
* This shader is intended for use as a plugin for the 'FinalOutputFormattingBlit'
* chain of the Psychtoolbox-3 imaging pipeline and used for the PsychImaging
* task 'UseSubpixelDrive'.
*
* (c) 2017 by Mario Kleiner, part of PTB-3, licensed to you under MIT license.
* See file License.txt in the Psychtoolbox root folder for the license.
*/
#extension GL_ARB_texture_rectangle : enable
uniform sampler2DRect Image;
void main()
{
/* Get output framebuffer pixel position (x,y): x is column, y is row of image. */
vec2 outpos = gl_FragCoord.xy;
/* We sample horizontal groups of 3 adjacent input texels for one output pixel. */
outpos.x = floor(outpos.x) * 3.0;
/* Sample red channel (=luminance) at three horizontal offsets and pack into 1 pixel. */
gl_FragColor.r = texture2DRect(Image, vec2(outpos.x + 0.5, outpos.y + 0.5)).r;
gl_FragColor.g = texture2DRect(Image, vec2(outpos.x + 1.5, outpos.y + 0.5)).r;
gl_FragColor.b = texture2DRect(Image, vec2(outpos.x + 2.5, outpos.y + 0.5)).r;
}
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