1 | uniform sampler2D u_image;
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2 | varying vec2 v_pos;
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3 |
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4 | uniform vec2 u_latrange;
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5 | uniform vec2 u_light;
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6 | uniform vec4 u_shadow;
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7 | uniform vec4 u_highlight;
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8 | uniform vec4 u_accent;
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9 |
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10 |
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11 |
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12 | void main() {
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13 | vec4 pixel = texture2D(u_image, v_pos);
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14 |
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15 | vec2 deriv = ((pixel.rg * 2.0) - 1.0);
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16 |
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17 | // We divide the slope by a scale factor based on the cosin of the pixel's approximate latitude
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18 | // to account for mercator projection distortion. see #4807 for details
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19 | float scaleFactor = cos(radians((u_latrange[0] - u_latrange[1]) * (1.0 - v_pos.y) + u_latrange[1]));
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20 | // We also multiply the slope by an arbitrary z-factor of 1.25
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21 | float slope = atan(1.25 * length(deriv) / scaleFactor);
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22 | float aspect = deriv.x != 0.0 ? atan(deriv.y, -deriv.x) : PI / 2.0 * (deriv.y > 0.0 ? 1.0 : -1.0);
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23 |
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24 | float intensity = u_light.x;
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25 | // We add PI to make this property match the global light object, which adds PI/2 to the light's azimuthal
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26 | // position property to account for 0deg corresponding to north/the top of the viewport in the style spec
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27 | // and the original shader was written to accept (-illuminationDirection - 90) as the azimuthal.
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28 | float azimuth = u_light.y + PI;
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29 |
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30 | // We scale the slope exponentially based on intensity, using a calculation similar to
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31 | // the exponential interpolation function in the style spec:
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32 | // src/style-spec/expression/definitions/interpolate.js#L217-L228
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33 | // so that higher intensity values create more opaque hillshading.
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34 | float base = 1.875 - intensity * 1.75;
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35 | float maxValue = 0.5 * PI;
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36 | float scaledSlope = intensity != 0.5 ? ((pow(base, slope) - 1.0) / (pow(base, maxValue) - 1.0)) * maxValue : slope;
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37 |
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38 | // The accent color is calculated with the cosine of the slope while the shade color is calculated with the sine
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39 | // so that the accent color's rate of change eases in while the shade color's eases out.
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40 | float accent = cos(scaledSlope);
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41 | // We multiply both the accent and shade color by a clamped intensity value
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42 | // so that intensities >= 0.5 do not additionally affect the color values
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43 | // while intensity values < 0.5 make the overall color more transparent.
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44 | vec4 accent_color = (1.0 - accent) * u_accent * clamp(intensity * 2.0, 0.0, 1.0);
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45 | float shade = abs(mod((aspect + azimuth) / PI + 0.5, 2.0) - 1.0);
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46 | vec4 shade_color = mix(u_shadow, u_highlight, shade) * sin(scaledSlope) * clamp(intensity * 2.0, 0.0, 1.0);
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47 | gl_FragColor = accent_color * (1.0 - shade_color.a) + shade_color;
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48 |
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49 |
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50 | gl_FragColor = vec4(1.0);
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51 |
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52 | }
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