uniform sampler2D heights;
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uniform sampler2D colors;
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// This material expects heights to be sorted from lowest to highest.
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float getHeight(int idx, float invTexSize)
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{
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vec2 uv = vec2((float(idx) + 0.5) * invTexSize, 0.5);
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#ifdef OES_texture_float
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return texture2D(heights, uv).x;
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#else
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return czm_unpackFloat(texture2D(heights, uv));
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#endif
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}
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czm_material czm_getMaterial(czm_materialInput materialInput)
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{
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czm_material material = czm_getDefaultMaterial(materialInput);
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float height = materialInput.height;
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float invTexSize = 1.0 / float(heightsDimensions.x);
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float minHeight = getHeight(0, invTexSize);
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float maxHeight = getHeight(heightsDimensions.x - 1, invTexSize);
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// early-out when outside the height range
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if (height < minHeight || height > maxHeight) {
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material.diffuse = vec3(0.0);
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material.alpha = 0.0;
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return material;
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}
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// Binary search to find heights above and below.
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int idxBelow = 0;
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int idxAbove = heightsDimensions.x;
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float heightBelow = minHeight;
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float heightAbove = maxHeight;
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// while loop not allowed, so use for loop with max iterations.
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// maxIterations of 16 supports a texture size up to 65536 (2^16).
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const int maxIterations = 16;
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for (int i = 0; i < maxIterations; i++) {
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if (idxBelow >= idxAbove - 1) {
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break;
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}
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int idxMid = (idxBelow + idxAbove) / 2;
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float heightTex = getHeight(idxMid, invTexSize);
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if (height > heightTex) {
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idxBelow = idxMid;
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heightBelow = heightTex;
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} else {
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idxAbove = idxMid;
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heightAbove = heightTex;
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}
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}
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float lerper = heightBelow == heightAbove ? 1.0 : (height - heightBelow) / (heightAbove - heightBelow);
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vec2 colorUv = vec2(invTexSize * (float(idxBelow) + 0.5 + lerper), 0.5);
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vec4 color = texture2D(colors, colorUv);
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// undo preumultiplied alpha
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if (color.a > 0.0)
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{
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color.rgb /= color.a;
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}
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color.rgb = czm_gammaCorrect(color.rgb);
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material.diffuse = color.rgb;
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material.alpha = color.a;
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return material;
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}
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