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#version 120
varying highp vec3 pos;
uniform highp sampler3D textureSampler;
uniform highp vec3 cameraPositionRelativeToModel;
uniform highp vec4 colorIndex[256];
uniform highp int color8Bit;
const float maxDist = sqrt(2.0);
const int sampleCount = 1024;
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 object
highp vec3 rayDir = -(cameraPositionRelativeToModel - pos);
highp vec3 invRayDir = 1.0 / rayDir;
highp vec3 minCorner = vec3(-1.0);
highp vec3 maxCorner = vec3(1.0);
highp vec3 t1 = invRayDir * (minCorner - pos);
highp vec3 t2 = invRayDir * (maxCorner - pos);
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 rayStart = pos;
// Flip Y and Z so QImage bits work directly for texture and first image is in the front
rayStart.yz = -rayStart.yz;
highp vec3 rayStop = pos + rayDir * tFar;
rayStop.yz = -rayStop.yz;
// Convert intersections to texture coords
rayStart = 0.5 * (rayStart + 1.0);
rayStop = 0.5 * (rayStop + 1.0);
highp vec3 curPos = rayStart;
highp float fullDist = distance(rayStop, rayStart);
highp float stepSize = maxDist / float(sampleCount); // TODO: Stepsize needs to be improved
highp vec3 step = normalize(rayStop - rayStart) * stepSize;
highp float totalDist = 0.0;
highp float totalAlpha = 0.0;
highp vec4 destColor = vec4(0, 0, 0, 0);
highp vec4 curColor = vec4(0, 0, 0, 0);
highp vec3 curRgb = vec3(0, 0, 0);
highp float curAlpha = 0.0;
for (int i = 0; i < sampleCount; i++) {
curColor = texture3D(textureSampler, curPos);
if (color8Bit != 0)
curColor = colorIndex[int(curColor.r * 255.0)];
curAlpha = curColor.a;
if (curAlpha > alphaThreshold) {
curRgb = curColor.rgb * curAlpha * (1.0 - totalAlpha);
destColor.rgb += curRgb;
totalAlpha += curAlpha;
}
curPos += step;
totalDist += stepSize;
if (totalDist > fullDist || totalAlpha >= 1.0) {
break;
}
}
destColor.a = totalAlpha;
gl_FragColor = clamp(destColor, 0.0, 1.0);
}
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