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/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/*
* This file is part of the LibreOffice project.
*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
*/
/* TODO Use textureOffset for newest version of GLSL */
uniform sampler2D sampler;
uniform int swidth;
uniform int sheight;
uniform float xscale;
uniform float yscale;
uniform float xsrcconvert;
uniform float ysrcconvert;
uniform float xdestconvert;
uniform float ydestconvert;
varying vec2 tex_coord;
void main(void)
{
// Convert to pixel coordinates again.
int dx = int( tex_coord.s * xdestconvert );
int dy = int( tex_coord.t * ydestconvert );
// Note: These values are always the same for the same X (or Y),
// so they could be precalculated in C++ and passed to the shader,
// but GLSL has limits on the size of uniforms passed to it,
// so it'd need something like texture buffer objects from newer
// GLSL versions, and it seems the hassle is not really worth it.
// How much each column/row will contribute to the resulting pixel.
// assert( xscale <= 100 ); assert( yscale <= 100 );
float xratio[ 100 + 2 ];
float yratio[ 100 + 2 ];
// For finding the first and last source pixel.
int xpixel[ 100 + 2 ];
int ypixel[ 100 + 2 ];
int xpos = 0;
int ypos = 0;
// Compute the range of source pixels which will make up this destination pixel.
float fsx1 = dx * xscale;
float fsx2 = fsx1 + xscale;
// To whole pixel coordinates.
int sx1 = ceil( fsx1 );
int sx2 = floor( fsx2 );
// Range checking.
sx2 = min( sx2, swidth - 1 );
sx1 = min( sx1, sx2 );
// How much one full column contributes to the resulting pixel.
float width = min( xscale, swidth - fsx1 );
if( sx1 - fsx1 > 0.001 )
{ // The first column contributes only partially.
xpixel[ xpos ] = sx1 - 1;
xratio[ xpos ] = ( sx1 - fsx1 ) / width;
++xpos;
}
for( int sx = sx1; sx < sx2; ++sx )
{ // Columns that fully contribute to the resulting pixel.
xpixel[ xpos ] = sx;
xratio[ xpos ] = 1.0 / width;
++xpos;
}
if( fsx2 - sx2 > 0.001 )
{ // The last column contributes only partially.
xpixel[ xpos ] = sx2;
xratio[ xpos ] = min( min( fsx2 - sx2, 1.0 ) / width, 1.0 );
++xpos;
}
// The same for Y.
float fsy1 = dy * yscale;
float fsy2 = fsy1 + yscale;
int sy1 = ceil( fsy1 );
int sy2 = floor( fsy2 );
sy2 = min( sy2, sheight - 1 );
sy1 = min( sy1, sy2 );
float height = min( yscale, sheight - fsy1 );
if( sy1 - fsy1 > 0.001 )
{
ypixel[ ypos ] = sy1 - 1;
yratio[ ypos ] = ( sy1 - fsy1 ) / height;
++ypos;
}
for( int sy = sy1; sy < sy2; ++sy )
{
ypixel[ ypos ] = sy;
yratio[ ypos ] = 1.0 / height;
++ypos;
}
if( fsy2 - sy2 > 0.001 )
{
ypixel[ ypos ] = sy2;
yratio[ ypos ] = min( min( fsy2 - sy2, 1.0 ) / height, 1.0 );
++ypos;
}
int xstart = xpixel[ 0 ];
int xend = xpixel[ xpos - 1 ];
int ystart = ypixel[ 0 ];
int yend = ypixel[ ypos - 1 ];
vec4 sum = vec4( 0.0, 0.0, 0.0, 0.0 );
ypos = 0;
for( int y = ystart; y <= yend; ++y, ++ypos )
{
vec4 tmp = vec4( 0.0, 0.0, 0.0, 0.0 );
xpos = 0;
for( int x = xstart; x <= xend; ++x, ++xpos )
{
vec2 offset = vec2( x * xsrcconvert, y * ysrcconvert );
tmp += texture2D( sampler, offset ) * xratio[ xpos ];
}
sum += tmp * yratio[ ypos ];
}
gl_FragColor = sum;
}
/* vim:set shiftwidth=4 softtabstop=4 expandtab: */
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