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// NOTE: DO NOT CHANGE THIS FILE. IT IS AUTOMATICALLY GENERATED.
#include <mbgl/shaders/hillshade_prepare.hpp>
#include <mbgl/shaders/source.hpp>
namespace mbgl {
namespace shaders {
const char* hillshade_prepare::name = "hillshade_prepare";
const char* hillshade_prepare::vertexSource = source() + 27925;
const char* hillshade_prepare::fragmentSource = source() + 28218;
// Uncompressed source of hillshade_prepare.vertex.glsl:
/*
uniform mat4 u_matrix;
uniform vec2 u_dimension;
attribute vec2 a_pos;
attribute vec2 a_texture_pos;
varying vec2 v_pos;
void main() {
gl_Position = u_matrix * vec4(a_pos, 0, 1);
highp vec2 epsilon = 1.0 / u_dimension;
float scale = (u_dimension.x - 2.0) / u_dimension.x;
v_pos = (a_texture_pos / 8192.0) * scale + epsilon;
}
*/
// Uncompressed source of hillshade_prepare.fragment.glsl:
/*
#ifdef GL_ES
precision highp float;
#endif
uniform sampler2D u_image;
varying vec2 v_pos;
uniform vec2 u_dimension;
uniform float u_zoom;
uniform float u_maxzoom;
float getElevation(vec2 coord, float bias) {
// Convert encoded elevation value to meters
vec4 data = texture2D(u_image, coord) * 255.0;
return (data.r + data.g * 256.0 + data.b * 256.0 * 256.0) / 4.0;
}
void main() {
vec2 epsilon = 1.0 / u_dimension;
// queried pixels:
// +-----------+
// | | | |
// | a | b | c |
// | | | |
// +-----------+
// | | | |
// | d | e | f |
// | | | |
// +-----------+
// | | | |
// | g | h | i |
// | | | |
// +-----------+
float a = getElevation(v_pos + vec2(-epsilon.x, -epsilon.y), 0.0);
float b = getElevation(v_pos + vec2(0, -epsilon.y), 0.0);
float c = getElevation(v_pos + vec2(epsilon.x, -epsilon.y), 0.0);
float d = getElevation(v_pos + vec2(-epsilon.x, 0), 0.0);
float e = getElevation(v_pos, 0.0);
float f = getElevation(v_pos + vec2(epsilon.x, 0), 0.0);
float g = getElevation(v_pos + vec2(-epsilon.x, epsilon.y), 0.0);
float h = getElevation(v_pos + vec2(0, epsilon.y), 0.0);
float i = getElevation(v_pos + vec2(epsilon.x, epsilon.y), 0.0);
// here we divide the x and y slopes by 8 * pixel size
// where pixel size (aka meters/pixel) is:
// circumference of the world / (pixels per tile * number of tiles)
// which is equivalent to: 8 * 40075016.6855785 / (512 * pow(2, u_zoom))
// which can be reduced to: pow(2, 19.25619978527 - u_zoom)
// we want to vertically exaggerate the hillshading though, because otherwise
// it is barely noticeable at low zooms. to do this, we multiply this by some
// scale factor pow(2, (u_zoom - u_maxzoom) * a) where a is an arbitrary value
// Here we use a=0.3 which works out to the expression below. see
// nickidlugash's awesome breakdown for more info
// https://github.com/mapbox/mapbox-gl-js/pull/5286#discussion_r148419556
float exaggeration = u_zoom < 2.0 ? 0.4 : u_zoom < 4.5 ? 0.35 : 0.3;
vec2 deriv = vec2(
(c + f + f + i) - (a + d + d + g),
(g + h + h + i) - (a + b + b + c)
) / pow(2.0, (u_zoom - u_maxzoom) * exaggeration + 19.2562 - u_zoom);
gl_FragColor = clamp(vec4(
deriv.x / 2.0 + 0.5,
deriv.y / 2.0 + 0.5,
1.0,
1.0), 0.0, 1.0);
#ifdef OVERDRAW_INSPECTOR
gl_FragColor = vec4(1.0);
#endif
}
*/
} // namespace shaders
} // namespace mbgl
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