1 files changed, 80 insertions, 0 deletions
diff --git a/src/mbgl/shaders/hillshade.cpp b/src/mbgl/shaders/hillshade.cpp
new file mode 100644
index 0000000000..4083faa4b4
--- /dev/null
+++ b/src/mbgl/shaders/hillshade.cpp
@@ -0,0 +1,80 @@
+// NOTE: DO NOT CHANGE THIS FILE. IT IS AUTOMATICALLY GENERATED.
+
+#include <mbgl/shaders/hillshade.hpp>
+
+namespace mbgl {
+namespace shaders {
+
+const char* hillshade::name = "hillshade";
+const char* hillshade::vertexSource = R"MBGL_SHADER(
+uniform mat4 u_matrix;
+
+attribute vec2 a_pos;
+attribute vec2 a_texture_pos;
+
+varying vec2 v_pos;
+
+void main() {
+    gl_Position = u_matrix * vec4(a_pos, 0, 1);
+    v_pos = a_texture_pos / 8192.0;
+}
+
+)MBGL_SHADER";
+const char* hillshade::fragmentSource = R"MBGL_SHADER(
+uniform sampler2D u_image;
+varying vec2 v_pos;
+
+uniform vec2 u_latrange;
+uniform vec2 u_light;
+uniform vec4 u_shadow;
+uniform vec4 u_highlight;
+uniform vec4 u_accent;
+
+#define PI 3.141592653589793
+
+void main() {
+    vec4 pixel = texture2D(u_image, v_pos);
+
+    vec2 deriv = ((pixel.rg * 2.0) - 1.0);
+
+    // We divide the slope by a scale factor based on the cosin of the pixel's approximate latitude
+    // to account for mercator projection distortion. see #4807 for details
+    float scaleFactor = cos(radians((u_latrange[0] - u_latrange[1]) * (1.0 - v_pos.y) + u_latrange[1]));
+    // We also multiply the slope by an arbitrary z-factor of 1.25
+    float slope = atan(1.25 * length(deriv) / scaleFactor);
+    float aspect = deriv.x != 0.0 ? atan(deriv.y, -deriv.x) : PI / 2.0 * (deriv.y > 0.0 ? 1.0 : -1.0);
+
+    float intensity = u_light.x;
+    // We add PI to make this property match the global light object, which adds PI/2 to the light's azimuthal
+    // position property to account for 0deg corresponding to north/the top of the viewport in the style spec
+    // and the original shader was written to accept (-illuminationDirection - 90) as the azimuthal.
+    float azimuth = u_light.y + PI;
+
+    // We scale the slope exponentially based on intensity, using a calculation similar to
+    // the exponential interpolation function in the style spec:
+    // https://github.com/mapbox/mapbox-gl-js/blob/master/src/style-spec/expression/definitions/interpolate.js#L217-L228
+    // so that higher intensity values create more opaque hillshading.
+    float base = 1.875 - intensity * 1.75;
+    float maxValue = 0.5 * PI;
+    float scaledSlope = intensity != 0.5 ? ((pow(base, slope) - 1.0) / (pow(base, maxValue) - 1.0)) * maxValue : slope;
+
+    // The accent color is calculated with the cosine of the slope while the shade color is calculated with the sine
+    // so that the accent color's rate of change eases in while the shade color's eases out.
+    float accent = cos(scaledSlope);
+    // We multiply both the accent and shade color by a clamped intensity value
+    // so that intensities >= 0.5 do not additionally affect the color values
+    // while intensity values < 0.5 make the overall color more transparent.
+    vec4 accent_color = (1.0 - accent) * u_accent * clamp(intensity * 2.0, 0.0, 1.0);
+    float shade = abs(mod((aspect + azimuth) / PI + 0.5, 2.0) - 1.0);
+    vec4 shade_color = mix(u_shadow, u_highlight, shade) * sin(scaledSlope) * clamp(intensity * 2.0, 0.0, 1.0);
+    gl_FragColor = accent_color * (1.0 - shade_color.a) + shade_color;
+
+#ifdef OVERDRAW_INSPECTOR
+    gl_FragColor = vec4(1.0);
+#endif
+}
+
+)MBGL_SHADER";
+
+} // namespace shaders
+} // namespace mbgl