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++ VARYING vec3 pos;
++ VARYING vec3 rayDir;
++
++ const highp vec3 xPlaneNormal = vec3(1.0, 0, 0);
++ const highp vec3 yPlaneNormal = vec3(0, 1.0, 0);
++ const highp vec3 zPlaneNormal = vec3(0, 0, 1.0);
++
++ void MAIN() {
++ // Find out where ray intersects the slice planes
++ vec3 normRayDir = normalize(rayDir);
++ highp vec3 rayStart = pos;
++ highp float minT = 2.0;
++ if (normRayDir.x != 0.0 && normRayDir.y != 0.0 && normRayDir.z != 0.0) {
++ highp vec3 boxBounds = vec3(1.0, 1.0, 1.0);
++ highp vec3 invRayDir = 1.0 / normRayDir;
++ if (normRayDir.x < 0)
++ boxBounds.x = -1.0;
++ if (normRayDir.y < 0)
++ boxBounds.y = -1.0;
++ if (normRayDir.z < 0)
++ boxBounds.z = -1.0;
++ highp vec3 t = (boxBounds - rayStart) * invRayDir;
++ minT = min(t.x, min(t.y, t.z));
++ }
++
++ highp vec3 xPoint = vec3(volumeSliceIndices.x, 0, 0);
++ highp vec3 yPoint = vec3(0, volumeSliceIndices.y, 0);
++ highp vec3 zPoint = vec3(0, 0, volumeSliceIndices.z);
++ highp float firstD = minT + 1.0;
++ highp float secondD = firstD;
++ highp float thirdD = firstD;
++ if (volumeSliceIndices.x >= -1.0) {
++ highp float dx = dot(xPoint - rayStart, xPlaneNormal) / dot(normRayDir, xPlaneNormal);
++ if (dx >= 0.0 && dx <= minT)
++ firstD = min(dx, firstD);
++ }
++ if (volumeSliceIndices.y >= -1.0) {
++ highp float dy = dot(yPoint - rayStart, yPlaneNormal) / dot(normRayDir, yPlaneNormal);
++ if (dy >= 0.0 && dy <= minT) {
++ if (dy < firstD) {
++ secondD = firstD;
++ firstD = dy;
++ } else {
++ secondD = dy;
++ }
++ }
++ }
++ if (volumeSliceIndices.z >= -1.0) {
++ highp float dz = dot(zPoint - rayStart, zPlaneNormal) / dot(normRayDir, zPlaneNormal);
++ if (dz >= 0.0) {
++ if (dz < firstD && dz <= minT) {
++ thirdD = secondD;
++ secondD = firstD;
++ firstD = dz;
++ } else if (dz < secondD){
++ thirdD = secondD;
++ secondD = dz;
++ } else {
++ thirdD = dz;
++ }
++ }
++ }
++
++ highp vec4 destColor = vec4(0.0, 0.0, 0.0, 0.0);
++ highp vec4 curColor = vec4(0.0, 0.0, 0.0, 0.0);
++ highp float totalAlpha = 0.0;
++ highp vec3 curRgb = vec3(0, 0, 0);
++ highp float curAlpha = 0.0;
++
++ // Convert intersection to texture coords
++
++ if (firstD <= minT) {
++ highp vec3 texelVec = rayStart + normRayDir * firstD;
++ if (clamp(texelVec.x, minBounds.x, maxBounds.x) == texelVec.x
++ && clamp(texelVec.y, maxBounds.y, minBounds.y) == texelVec.y
++ && clamp(texelVec.z, maxBounds.z, minBounds.z) == texelVec.z) {
++ texelVec = 0.5 * (texelVec + 1.0);
++ curColor = textureLod(textureSampler, texelVec, 0);
++ if (color8Bit != 0)
++ curColor = textureLod(colorSampler, vec2(curColor.r, 0), 0);
++
++ if (curColor.a > 0.0) {
++ curAlpha = curColor.a;
++ if (curColor.a == 1.0 && preserveOpacity != 0)
++ curAlpha = 1.0;
++ else
++ curAlpha = clamp(curColor.a * alphaMultiplier, 0.0, 1.0);
++ destColor.rgb = curColor.rgb * curAlpha;
++ totalAlpha = curAlpha;
++ }
++ }
++ if (secondD <= minT && totalAlpha < 1.0) {
++ texelVec = rayStart + normRayDir * secondD;
++ if (clamp(texelVec.x, minBounds.x, maxBounds.x) == texelVec.x
++ && clamp(texelVec.y, maxBounds.y, minBounds.y) == texelVec.y
++ && clamp(texelVec.z, maxBounds.z, minBounds.z) == texelVec.z) {
++ texelVec = 0.5 * (texelVec + 1.0);
++ curColor = textureLod(textureSampler, texelVec, 0);
++ if (color8Bit != 0)
++ curColor = textureLod(colorSampler, vec2(curColor.r, 0), 0);
++ if (curColor.a > 0.0) {
++ if (curColor.a == 1.0 && preserveOpacity != 0)
++ curAlpha = 1.0;
++ else
++ curAlpha = clamp(curColor.a * alphaMultiplier, 0.0, 1.0);
++ curRgb = curColor.rgb * curAlpha * (1.0 - totalAlpha);
++ destColor.rgb += curRgb;
++ totalAlpha += curAlpha;
++ }
++ }
++ if (thirdD <= minT && totalAlpha < 1.0) {
++ texelVec = rayStart + normRayDir * thirdD;
++ if (clamp(texelVec.x, minBounds.x, maxBounds.x) == texelVec.x
++ && clamp(texelVec.y, maxBounds.y, minBounds.y) == texelVec.y
++ && clamp(texelVec.z, maxBounds.z, minBounds.z) == texelVec.z) {
++ texelVec = 0.5 * (texelVec + 1.0);
++ curColor = textureLod(textureSampler, texelVec, 0);
++ if (curColor.a > 0.0) {
++ if (color8Bit != 0)
++ curColor = textureLod(colorSampler, vec2(curColor.r, 0), 0);
++ if (curColor.a == 1.0 && preserveOpacity != 0)
++ curAlpha = 1.0;
++ else
++ curAlpha = clamp(curColor.a * alphaMultiplier, 0.0, 1.0);
++ curRgb = curColor.rgb * curAlpha * (1.0 - totalAlpha);
++ destColor.rgb += curRgb;
++ totalAlpha += curAlpha;
++ }
++ }
++ }
++ }
++ }
++
++ if (totalAlpha == 0.0)
++ discard;
++
++ // Brighten up the final color if there is some transparency left
++ if (totalAlpha > 0.0 && totalAlpha < 1.0)
++ destColor *= 1.0 / totalAlpha;
++
++ destColor.a = totalAlpha;
++ FRAGCOLOR = clamp(destColor, 0.0, 1.0);
++ }
++