76 lines
2.6 KiB
GLSL
76 lines
2.6 KiB
GLSL
#ifdef GL_ES
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precision highp float;
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#endif
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in vec2 v_pos;
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uniform sampler2D u_image;
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layout (std140) uniform HillshadePrepareTilePropsUBO {
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highp vec4 u_unpack;
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highp vec2 u_dimension;
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highp float u_zoom;
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highp float u_maxzoom;
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};
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float getElevation(vec2 coord, float bias) {
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// Convert encoded elevation value to meters
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vec4 data = texture(u_image, coord) * 255.0;
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data.a = -1.0;
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return dot(data, u_unpack);
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}
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void main() {
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vec2 epsilon = 1.0 / u_dimension;
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float tileSize = u_dimension.x - 2.0;
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// queried pixels (using Sobel operator kernel):
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// +-----------+
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// | | | |
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// | a | b | c |
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// | | | |
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// +-----------+
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// | | | |
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// | d | e | f |
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// | | | |
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// +-----------+
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// | | | |
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// | g | h | i |
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// | | | |
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// +-----------+
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float a = getElevation(v_pos + vec2(-epsilon.x, -epsilon.y), 0.0);
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float b = getElevation(v_pos + vec2(0, -epsilon.y), 0.0);
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float c = getElevation(v_pos + vec2(epsilon.x, -epsilon.y), 0.0);
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float d = getElevation(v_pos + vec2(-epsilon.x, 0), 0.0);
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//float e = getElevation(v_pos, 0.0);
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float f = getElevation(v_pos + vec2(epsilon.x, 0), 0.0);
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float g = getElevation(v_pos + vec2(-epsilon.x, epsilon.y), 0.0);
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float h = getElevation(v_pos + vec2(0, epsilon.y), 0.0);
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float i = getElevation(v_pos + vec2(epsilon.x, epsilon.y), 0.0);
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// Convert the raw pixel-space derivative (slope) into world-space slope.
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// The conversion factor is: tileSize / (8 * meters_per_pixel).
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// meters_per_pixel is calculated as pow(2.0, 28.2562 - u_zoom).
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// The exaggeration factor is applied to scale the effect at lower zooms.
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// See nickidlugash's awesome breakdown for more info
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// https://github.com/mapbox/mapbox-gl-js/pull/5286#discussion_r148419556
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float exaggerationFactor = u_zoom < 2.0 ? 0.4 : u_zoom < 4.5 ? 0.35 : 0.3;
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float exaggeration = u_zoom < 15.0 ? (u_zoom - 15.0) * exaggerationFactor : 0.0;
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vec2 deriv = vec2(
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(c + f + f + i) - (a + d + d + g),
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(g + h + h + i) - (a + b + b + c)
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) * tileSize / pow(2.0, exaggeration + (28.2562 - u_zoom));
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// Encode the derivative into the color channels (r and g)
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// The derivative is scaled from world-space slope to the range [0, 1] for texture storage.
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// The maximum possible world-space derivative is assumed to be 4 (hence division by 8.0).
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fragColor = clamp(vec4(
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deriv.x / 8.0 + 0.5,
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deriv.y / 8.0 + 0.5,
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1.0,
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1.0), 0.0, 1.0);
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#ifdef OVERDRAW_INSPECTOR
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fragColor = vec4(1.0);
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#endif
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}
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