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99 lines
2.0 KiB
C++
99 lines
2.0 KiB
C++
#include <cmath>
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#include "hillshading.h"
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struct Constants
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{
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double a1;
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double a2;
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double a3;
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};
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struct SubMatrix
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{
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double z1;
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double z2;
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double z3;
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double z4;
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double z6;
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double z7;
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double z8;
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double z9;
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};
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struct Derivatives
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{
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double dzdx;
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double dzdy;
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};
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static void getConstants(double azimuth, double elevation, Constants &c)
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{
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double alpha = (M_PI / 180.0) * azimuth;
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double beta = (M_PI / 180.0) * elevation;
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c.a1 = sin(beta);
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c.a2 = cos(beta) * sin(alpha);
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c.a3 = cos(beta) * cos(alpha);
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}
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static void getDerivativesHorn(const SubMatrix &sm, double z, Derivatives &d)
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{
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d.dzdx = (z * (sm.z3 + 2 * sm.z6 + sm.z9 - sm.z1 - 2 * sm.z4 - sm.z7)) / 8;
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d.dzdy = (z * (sm.z1 + 2 * sm.z2 + sm.z3 - sm.z7 - 2 * sm.z8 - sm.z9)) / 8;
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}
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static void getSubmatrix(int x, int y, const MatrixD &m, SubMatrix &sm)
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{
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int left = x - 1;
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int right = x + 1;
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int top = y - 1;
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int bottom = y + 1;
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sm.z1 = m.at(top, left);
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sm.z2 = m.at(top, x);
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sm.z3 = m.at(top, right);
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sm.z4 = m.at(y, left);
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sm.z6 = m.at(y, right);
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sm.z7 = m.at(bottom, left);
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sm.z8 = m.at(bottom, x);
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sm.z9 = m.at(bottom, right);
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}
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QImage HillShading::render(const MatrixD &m, int extend, quint8 alpha, double z,
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double azimuth, double elevation)
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{
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QImage img(m.w() - 2 * extend, m.h() - 2 * extend,
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QImage::Format_ARGB32_Premultiplied);
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uchar *bits = img.bits();
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int bpl = img.bytesPerLine();
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Constants c;
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SubMatrix sm;
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Derivatives d;
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getConstants(azimuth, elevation, c);
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for (int y = extend; y < m.h() - extend; y++) {
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for (int x = extend; x < m.w() - extend; x++) {
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getSubmatrix(x, y, m, sm);
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getDerivativesHorn(sm, z, d);
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double L = (c.a1 - c.a2 * d.dzdx - c.a3 * d.dzdy)
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/ sqrt(1.0 + d.dzdx * d.dzdx + d.dzdy * d.dzdy);
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quint32 pixel;
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if (std::isnan(L))
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pixel = 0;
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else {
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L = sqrt(L * 0.8 + 0.2);
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quint8 val = (L < 0) ? 0 : L * alpha;
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pixel = (alpha - val)<<24;
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}
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*(quint32*)(bits + (y - extend) * bpl + (x - extend) * 4) = pixel;
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}
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}
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return img;
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}
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