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#version 120
varying highp vec3 pos;
uniform highp sampler3D textureSampler;
uniform highp vec3 cameraPositionRelativeToModel;
uniform highp vec3 volumeSliceIndices;
uniform highp vec4 colorIndex[256];
uniform highp int color8Bit;
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);
const float alphaThreshold = 0.001;
void main() {
// Raytrace into volume, need to sample pixels along the eye ray until we hit opacity 1
// Find out where ray intersects the slice planes
highp vec3 rayDir = -(cameraPositionRelativeToModel - pos);
highp vec3 rayStart = pos;
// Flip Y and Z so QImage bits work directly for texture and first image is in the front
rayStart.yz = -rayStart.yz;
rayDir.yz = -rayDir.yz;
highp vec3 invRayDir = 1.0 / rayDir;
highp vec3 minCorner = vec3(-1.0);
highp vec3 maxCorner = vec3(1.0);
highp vec3 t1 = invRayDir * (minCorner - rayStart);
highp vec3 t2 = invRayDir * (maxCorner - rayStart);
highp vec3 tmin = min(t1, t2);
highp vec3 tmax = max(t1, t2);
highp vec2 t = max(tmin.xx, tmin.yz);
t = min(tmax.xx, tmax.yz);
float tFar = min(t.x, t.y);
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 = tFar + 1.0;
highp float secondD = firstD;
highp float thirdD = firstD;
if (volumeSliceIndices.x >= -1.0) {
highp float dx = dot(xPoint - rayStart, xPlaneNormal) / dot(rayDir, xPlaneNormal);
if (dx >= 0.0 && dx <= tFar)
firstD = min(dx, firstD);
}
if (volumeSliceIndices.y >= -1.0) {
highp float dy = dot(yPoint - rayStart, yPlaneNormal) / dot(rayDir, yPlaneNormal);
if (dy >= 0.0 && dy <= tFar) {
if (dy < firstD) {
secondD = firstD;
firstD = dy;
} else {
secondD = dy;
}
}
}
if (volumeSliceIndices.z >= -1.0) {
highp float dz = dot(zPoint - rayStart, zPlaneNormal) / dot(rayDir, zPlaneNormal);
if (dz >= 0.0) {
if (dz < firstD && dz <= tFar) {
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 float totalAlpha = 0.0;
highp vec3 curRgb = vec3(0, 0, 0);
// Convert intersection to texture coords
if (firstD <= tFar) {
highp vec3 firstTex = rayStart + rayDir * firstD;
firstTex = 0.5 * (firstTex + 1.0);
highp vec4 firstColor = texture3D(textureSampler, firstTex);
if (color8Bit != 0)
firstColor = colorIndex[int(firstColor.r * 255.0)];
if (firstColor.a > alphaThreshold) {
destColor.rgb = firstColor.rgb * firstColor.a;
totalAlpha = firstColor.a;
}
if (secondD <= tFar && totalAlpha < 1.0) {
highp vec3 secondTex = rayStart + rayDir * secondD;
secondTex = 0.5 * (secondTex + 1.0);
highp vec4 secondColor = texture3D(textureSampler, secondTex);
if (color8Bit != 0)
secondColor = colorIndex[int(secondColor.r * 255.0)];
if (secondColor.a > alphaThreshold) {
curRgb = secondColor.rgb * secondColor.a * (1.0 - totalAlpha);
destColor.rgb += curRgb;
totalAlpha += secondColor.a;
}
if (thirdD <= tFar && totalAlpha < 1.0) {
highp vec3 thirdTex = rayStart + rayDir * thirdD;
thirdTex = 0.5 * (thirdTex + 1.0);
highp vec4 thirdColor = texture3D(textureSampler, thirdTex);
if (color8Bit != 0)
thirdColor = colorIndex[int(thirdColor.r * 255.0)];
if (thirdColor.a > alphaThreshold) {
curRgb = thirdColor.rgb * thirdColor.a * (1.0 - totalAlpha);
destColor.rgb += curRgb;
totalAlpha += thirdColor.a;
}
}
}
}
destColor.a = totalAlpha;
gl_FragColor = clamp(destColor, 0.0, 1.0);
}
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