41 lines
1.9 KiB
Common Lisp
41 lines
1.9 KiB
Common Lisp
// Copyright 2017 The Servo Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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// Computes total coverage and writes into the output atlas for subpixel antialiasing.
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//
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// This proceeds top to bottom for better data locality. For details on the algorithm, see [1].
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//
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// [1]: https://medium.com/@raphlinus/inside-the-fastest-font-renderer-in-the-world-75ae5270c445
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const sampler_t SAMPLER = CLK_NORMALIZED_COORDS_FALSE | CLK_ADDRESS_NONE | CLK_FILTER_NEAREST;
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__kernel void accum_subpixel(__write_only image2d_t gImage,
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__read_only image2d_t gCoverage,
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uint4 kAtlasRect,
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uint kAtlasShelfHeight) {
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// Determine the boundaries of the column we'll be traversing.
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uint column = 0, firstRow = 0, lastRow = 0;
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get_location(&column, &firstRow, &lastRow, kAtlasRect, kAtlasShelfHeight);
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// Sweep down the column, accumulating coverage as we go.
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float3 coverage = (float3)(0.0f, 0.0f, 0.0f);
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for (uint row = firstRow; row < lastRow; row++) {
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int coverageColumn = (int)(column * 3);
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coverage.r += read_imagef(gCoverage, SAMPLER, (int2)(coverageColumn, (int)row)).r;
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coverage.g += read_imagef(gCoverage, SAMPLER, (int2)(coverageColumn + 1, (int)row)).r;
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coverage.b += read_imagef(gCoverage, SAMPLER, (int2)(coverageColumn + 2, (int)row)).r;
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int2 coord = (int2)((int)column, (int)row) + (int2)kAtlasRect.xy;
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float3 aa = fabs(coverage);
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write_imagef(gImage, coord, (float4)(aa, 1.0f));
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}
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}
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