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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;
uniform highp float alphaMultiplier;
uniform highp int preserveOpacity;
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
highp vec3 rayDir = -(cameraPositionRelativeToModel - pos);
rayDir = normalize(rayDir);
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 float minT = 2.0f;
if (rayDir.x != 0.0 && rayDir.y != 0.0 && rayDir.z != 0.0) {
highp vec3 boxBounds = vec3(1.0, 1.0, 1.0);
highp vec3 invRayDir = 1.0 / rayDir;
if (rayDir.x < 0)
boxBounds.x = -1.0;
if (rayDir.y < 0)
boxBounds.y = -1.0;
if (rayDir.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(rayDir, xPlaneNormal);
if (dx >= 0.0 && dx <= minT)
firstD = min(dx, firstD);
}
if (volumeSliceIndices.y >= -1.0) {
highp float dy = dot(yPoint - rayStart, yPlaneNormal) / dot(rayDir, 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(rayDir, 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 firstTex = rayStart + rayDir * firstD;
firstTex = 0.5 * (firstTex + 1.0);
curColor = texture3D(textureSampler, firstTex);
if (color8Bit != 0)
curColor = colorIndex[int(curColor.r * 255.0)];
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) {
highp vec3 secondTex = rayStart + rayDir * secondD;
secondTex = 0.5 * (secondTex + 1.0);
curColor = texture3D(textureSampler, secondTex);
if (color8Bit != 0)
curColor = colorIndex[int(curColor.r * 255.0)];
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) {
highp vec3 thirdTex = rayStart + rayDir * thirdD;
thirdTex = 0.5 * (thirdTex + 1.0);
curColor = texture3D(textureSampler, thirdTex);
if (curColor.a > 0.0) {
if (color8Bit != 0)
curColor = colorIndex[int(curColor.r * 255.0)];
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;
}
}
}
}
// 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;
gl_FragColor = clamp(destColor, 0.0, 1.0);
}
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