230 lines
6.5 KiB
C++
230 lines
6.5 KiB
C++
// This file is part of meshoptimizer library; see meshoptimizer.h for version/license details
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#include "meshoptimizer.h"
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#include <assert.h>
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#include <float.h>
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#include <string.h>
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// This work is based on:
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// Nicolas Capens. Advanced Rasterization. 2004
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namespace meshopt
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{
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const int kViewport = 256;
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struct OverdrawBuffer
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{
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float z[kViewport][kViewport][2];
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unsigned int overdraw[kViewport][kViewport][2];
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};
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#ifndef min
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#define min(a, b) ((a) < (b) ? (a) : (b))
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#endif
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#ifndef max
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#define max(a, b) ((a) > (b) ? (a) : (b))
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#endif
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static float computeDepthGradients(float& dzdx, float& dzdy, float x1, float y1, float z1, float x2, float y2, float z2, float x3, float y3, float z3)
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{
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// z2 = z1 + dzdx * (x2 - x1) + dzdy * (y2 - y1)
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// z3 = z1 + dzdx * (x3 - x1) + dzdy * (y3 - y1)
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// (x2-x1 y2-y1)(dzdx) = (z2-z1)
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// (x3-x1 y3-y1)(dzdy) (z3-z1)
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// we'll solve it with Cramer's rule
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float det = (x2 - x1) * (y3 - y1) - (y2 - y1) * (x3 - x1);
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float invdet = (det == 0) ? 0 : 1 / det;
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dzdx = (z2 - z1) * (y3 - y1) - (y2 - y1) * (z3 - z1) * invdet;
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dzdy = (x2 - x1) * (z3 - z1) - (z2 - z1) * (x3 - x1) * invdet;
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return det;
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}
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// half-space fixed point triangle rasterizer
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static void rasterize(OverdrawBuffer* buffer, float v1x, float v1y, float v1z, float v2x, float v2y, float v2z, float v3x, float v3y, float v3z)
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{
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// compute depth gradients
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float DZx, DZy;
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float det = computeDepthGradients(DZx, DZy, v1x, v1y, v1z, v2x, v2y, v2z, v3x, v3y, v3z);
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int sign = det > 0;
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// flip backfacing triangles to simplify rasterization logic
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if (sign)
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{
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// flipping v2 & v3 preserves depth gradients since they're based on v1
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float t;
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t = v2x, v2x = v3x, v3x = t;
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t = v2y, v2y = v3y, v3y = t;
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t = v2z, v2z = v3z, v3z = t;
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// flip depth since we rasterize backfacing triangles to second buffer with reverse Z; only v1z is used below
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v1z = kViewport - v1z;
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DZx = -DZx;
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DZy = -DZy;
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}
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// coordinates, 28.4 fixed point
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int X1 = int(16.0f * v1x + 0.5f);
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int X2 = int(16.0f * v2x + 0.5f);
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int X3 = int(16.0f * v3x + 0.5f);
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int Y1 = int(16.0f * v1y + 0.5f);
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int Y2 = int(16.0f * v2y + 0.5f);
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int Y3 = int(16.0f * v3y + 0.5f);
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// bounding rectangle, clipped against viewport
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// since we rasterize pixels with covered centers, min >0.5 should round up
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// as for max, due to top-left filling convention we will never rasterize right/bottom edges
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// so max >= 0.5 should round down
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int minx = max((min(X1, min(X2, X3)) + 7) >> 4, 0);
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int maxx = min((max(X1, max(X2, X3)) + 7) >> 4, kViewport);
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int miny = max((min(Y1, min(Y2, Y3)) + 7) >> 4, 0);
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int maxy = min((max(Y1, max(Y2, Y3)) + 7) >> 4, kViewport);
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// deltas, 28.4 fixed point
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int DX12 = X1 - X2;
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int DX23 = X2 - X3;
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int DX31 = X3 - X1;
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int DY12 = Y1 - Y2;
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int DY23 = Y2 - Y3;
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int DY31 = Y3 - Y1;
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// fill convention correction
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int TL1 = DY12 < 0 || (DY12 == 0 && DX12 > 0);
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int TL2 = DY23 < 0 || (DY23 == 0 && DX23 > 0);
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int TL3 = DY31 < 0 || (DY31 == 0 && DX31 > 0);
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// half edge equations, 24.8 fixed point
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// note that we offset minx/miny by half pixel since we want to rasterize pixels with covered centers
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int FX = (minx << 4) + 8;
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int FY = (miny << 4) + 8;
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int CY1 = DX12 * (FY - Y1) - DY12 * (FX - X1) + TL1 - 1;
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int CY2 = DX23 * (FY - Y2) - DY23 * (FX - X2) + TL2 - 1;
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int CY3 = DX31 * (FY - Y3) - DY31 * (FX - X3) + TL3 - 1;
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float ZY = v1z + (DZx * float(FX - X1) + DZy * float(FY - Y1)) * (1 / 16.f);
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for (int y = miny; y < maxy; y++)
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{
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int CX1 = CY1;
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int CX2 = CY2;
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int CX3 = CY3;
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float ZX = ZY;
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for (int x = minx; x < maxx; x++)
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{
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// check if all CXn are non-negative
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if ((CX1 | CX2 | CX3) >= 0)
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{
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if (ZX >= buffer->z[y][x][sign])
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{
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buffer->z[y][x][sign] = ZX;
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buffer->overdraw[y][x][sign]++;
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}
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}
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// signed left shift is UB for negative numbers so use unsigned-signed casts
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CX1 -= int(unsigned(DY12) << 4);
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CX2 -= int(unsigned(DY23) << 4);
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CX3 -= int(unsigned(DY31) << 4);
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ZX += DZx;
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}
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// signed left shift is UB for negative numbers so use unsigned-signed casts
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CY1 += int(unsigned(DX12) << 4);
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CY2 += int(unsigned(DX23) << 4);
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CY3 += int(unsigned(DX31) << 4);
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ZY += DZy;
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}
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}
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} // namespace meshopt
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meshopt_OverdrawStatistics meshopt_analyzeOverdraw(const unsigned int* indices, size_t index_count, const float* vertex_positions, size_t vertex_count, size_t vertex_positions_stride)
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{
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using namespace meshopt;
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assert(index_count % 3 == 0);
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assert(vertex_positions_stride >= 12 && vertex_positions_stride <= 256);
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assert(vertex_positions_stride % sizeof(float) == 0);
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meshopt_Allocator allocator;
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size_t vertex_stride_float = vertex_positions_stride / sizeof(float);
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meshopt_OverdrawStatistics result = {};
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float minv[3] = {FLT_MAX, FLT_MAX, FLT_MAX};
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float maxv[3] = {-FLT_MAX, -FLT_MAX, -FLT_MAX};
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for (size_t i = 0; i < vertex_count; ++i)
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{
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const float* v = vertex_positions + i * vertex_stride_float;
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for (int j = 0; j < 3; ++j)
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{
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minv[j] = min(minv[j], v[j]);
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maxv[j] = max(maxv[j], v[j]);
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}
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}
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float extent = max(maxv[0] - minv[0], max(maxv[1] - minv[1], maxv[2] - minv[2]));
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float scale = kViewport / extent;
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float* triangles = allocator.allocate<float>(index_count * 3);
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for (size_t i = 0; i < index_count; ++i)
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{
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unsigned int index = indices[i];
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assert(index < vertex_count);
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const float* v = vertex_positions + index * vertex_stride_float;
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triangles[i * 3 + 0] = (v[0] - minv[0]) * scale;
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triangles[i * 3 + 1] = (v[1] - minv[1]) * scale;
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triangles[i * 3 + 2] = (v[2] - minv[2]) * scale;
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}
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OverdrawBuffer* buffer = allocator.allocate<OverdrawBuffer>(1);
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for (int axis = 0; axis < 3; ++axis)
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{
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memset(buffer, 0, sizeof(OverdrawBuffer));
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for (size_t i = 0; i < index_count; i += 3)
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{
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const float* vn0 = &triangles[3 * (i + 0)];
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const float* vn1 = &triangles[3 * (i + 1)];
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const float* vn2 = &triangles[3 * (i + 2)];
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switch (axis)
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{
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case 0:
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rasterize(buffer, vn0[2], vn0[1], vn0[0], vn1[2], vn1[1], vn1[0], vn2[2], vn2[1], vn2[0]);
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break;
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case 1:
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rasterize(buffer, vn0[0], vn0[2], vn0[1], vn1[0], vn1[2], vn1[1], vn2[0], vn2[2], vn2[1]);
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break;
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case 2:
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rasterize(buffer, vn0[1], vn0[0], vn0[2], vn1[1], vn1[0], vn1[2], vn2[1], vn2[0], vn2[2]);
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break;
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}
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}
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for (int y = 0; y < kViewport; ++y)
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for (int x = 0; x < kViewport; ++x)
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for (int s = 0; s < 2; ++s)
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{
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unsigned int overdraw = buffer->overdraw[y][x][s];
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result.pixels_covered += overdraw > 0;
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result.pixels_shaded += overdraw;
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}
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}
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result.overdraw = result.pixels_covered ? float(result.pixels_shaded) / float(result.pixels_covered) : 0.f;
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return result;
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}
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