diff options
Diffstat (limited to 'src/datavisualization/engine/shaders/texture3d.frag')
-rw-r--r-- | src/datavisualization/engine/shaders/texture3d.frag | 162 |
1 files changed, 109 insertions, 53 deletions
diff --git a/src/datavisualization/engine/shaders/texture3d.frag b/src/datavisualization/engine/shaders/texture3d.frag index 1192ae85..6dd7f78c 100644 --- a/src/datavisualization/engine/shaders/texture3d.frag +++ b/src/datavisualization/engine/shaders/texture3d.frag @@ -11,7 +11,10 @@ uniform highp int sampleCount; // This is the maximum sample count uniform highp float alphaMultiplier; uniform highp int preserveOpacity; -const highp float alphaThreshold = 0.0001; +// Ray traveling straight through a single 'alpha thickness' applies 100% of the encountered alpha. +// Rays traveling shorter distances apply a fraction. This is used to normalize the alpha over +// entire volume, regardless of texture dimensions +const highp float alphaThicknesses = 32.0; void main() { highp vec3 rayDir = -(cameraPositionRelativeToModel - pos); @@ -41,69 +44,122 @@ void main() { if (rayDir.z < 0) boxBounds.z = -1.0; highp vec3 t = (boxBounds - rayStart) * invRayDir; - highp float minT = min(t.x, t.y); - minT = min(minT, t.z); + highp float minT = min(t.x, min(t.y, t.z)); rayStop = rayStart + minT * rayDir; } + // Convert intersections to texture coords + rayStart = 0.5 * (rayStart + 1.0); + rayStop = 0.5 * (rayStop + 1.0); + + highp vec3 ray = rayStop - rayStart; + + // Avoid artifacts from divisions by zero + if (ray.x == 0) + ray.x = 0.000000001; + if (ray.y == 0) + ray.y = 0.000000001; + if (ray.z == 0) + ray.z = 0.000000001; + + highp vec3 absRay = abs(ray); + highp vec3 invAbsRay = 1.0 / absRay; + highp float fullDist = length(ray); + highp vec3 curPos = rayStart; + + highp vec4 curColor = vec4(0, 0, 0, 0); + highp float curAlpha = 0.0; + highp float curLen = 0.0; + highp vec3 curRgb = vec3(0, 0, 0); + highp vec4 destColor = vec4(0, 0, 0, 0); - highp float totalAlpha = 0.0; - - if (rayStart != rayStop) { - // Convert intersections to texture coords - rayStart = 0.5 * (rayStart + 1.0); - rayStop = 0.5 * (rayStop + 1.0); - - highp vec3 ray = rayStop - rayStart; - highp float fullDist = abs(length(ray)); - highp float rayX = abs(ray.x) * textureDimensions.x; - highp float rayY = abs(ray.y) * textureDimensions.y; - highp float rayZ = abs(ray.z) * textureDimensions.z; - highp float maxRayDim = max(rayX, rayY); - maxRayDim = max(maxRayDim, rayZ); - int maxCount = int(floor(maxRayDim)); - - highp vec3 step = ray / maxRayDim; - highp float stepSize = fullDist / maxRayDim; - - rayStart += (step * 0.001); - highp vec3 curPos = rayStart; - - // Adjust alpha multiplier according to the step size to get uniform alpha effect - // regardless of the ray angle. - highp float totalAlphaMultiplier = (stepSize / (1.0 / sampleCount)) * alphaMultiplier; - - highp vec4 curColor = vec4(0, 0, 0, 0); - highp vec3 curRgb = vec3(0, 0, 0); - highp float curAlpha = 0.0; - - // Raytrace into volume, need to sample pixels along the eye ray until we hit opacity 1 - for (int i = 0; i < sampleCount; i++) { - curColor = texture3D(textureSampler, curPos); - if (color8Bit != 0) - curColor = colorIndex[int(curColor.r * 255.0)]; - - // Unless we have explicit alpha multiplier, we want to preserve opacity anyway - if (curColor.a == 1.0 && (preserveOpacity != 0 || alphaMultiplier == 1.0)) + highp float totalOpacity = 1.0; + highp float nextOpacity = 1.0; + + highp float extraAlphaMultiplier = fullDist * alphaThicknesses; + + // nextEdges vector indicates the next edges of the texel boundaries along each axis that + // the ray is about to cross. The first edges are offset by a fraction of a texel to + // avoid artifacts from rounding errors later. + highp vec3 nextEdges = vec3(floor(curPos.x / textureDimensions.x) * textureDimensions.x, + floor(curPos.y / textureDimensions.y) * textureDimensions.y, + floor(curPos.z / textureDimensions.z) * textureDimensions.z); + + highp vec3 textureSteps = textureDimensions; + highp vec3 textureOffset = textureDimensions * 0.001; + if (ray.x > 0) { + nextEdges.x += textureDimensions.x + textureOffset.x; + } else { + nextEdges.x -= textureOffset.x; + textureSteps.x = -textureDimensions.x; + } + if (ray.y > 0) { + nextEdges.y += textureDimensions.y + textureOffset.y; + } else { + nextEdges.y -= textureOffset.y; + textureSteps.y = -textureDimensions.y; + } + if (ray.z > 0) { + nextEdges.z += textureDimensions.z + textureOffset.z; + } else { + nextEdges.z -= textureOffset.z; + textureSteps.z = -textureDimensions.z; + } + + // Raytrace into volume, need to sample pixels along the eye ray until we hit opacity 1 + for (int i = 0; i < sampleCount; i++) { + curColor = texture3D(textureSampler, curPos); + if (color8Bit != 0) + curColor = colorIndex[int(curColor.r * 255.0)]; + + // Find which dimension has least to go to figure out the next step distance + highp vec3 delta = abs(nextEdges - curPos); + highp vec3 modDelta = delta * invAbsRay; + highp float minDelta = min(modDelta.x, min(modDelta.y, modDelta.z)); + highp float stepSize; + if (minDelta == modDelta.x) { + nextEdges.x += textureSteps.x; + stepSize = delta.x * invAbsRay.x; + } + if (minDelta == modDelta.y) { + nextEdges.y += textureSteps.y; + stepSize = delta.y * invAbsRay.y; + } + if (minDelta == modDelta.z) { + nextEdges.z += textureSteps.z; + stepSize = delta.z * invAbsRay.z; + } + + curPos += stepSize * ray; + curLen += stepSize; + + if (curColor.a >= 0.0) { + curAlpha = alphaMultiplier * curColor.a; + if (curAlpha >= 1.0 || (curColor.a == 1.0 && preserveOpacity == 1)) curAlpha = 1.0; else - curAlpha = clamp(curColor.a * totalAlphaMultiplier, 0.0, 1.0); - - if (curAlpha > alphaThreshold) { - curRgb = curColor.rgb * curAlpha * (1.0 - totalAlpha); - destColor.rgb += curRgb; - totalAlpha += curAlpha; + curAlpha = curAlpha * extraAlphaMultiplier * stepSize; + highp float nextOpacity = totalOpacity - curAlpha; + // If opacity goes beyond full opacity, we need to adjust current alpha according + // to the fraction of the distance the material is visible, so that we don't get + // box artifacts around texels. + if (nextOpacity < 0.0) { + curAlpha *= totalOpacity / curAlpha; + nextOpacity = 0.0; } - if (i == maxCount || totalAlpha >= 1.0) - break; - curPos += step; + curRgb = curColor.rgb * curAlpha * (totalOpacity + nextOpacity); + totalOpacity = nextOpacity; + destColor.rgb += curRgb; } + + if (curLen >= 1.0 || totalOpacity <= 0.0) + break; } // Brighten up the final color if there is some transparency left - if (totalAlpha > alphaThreshold && totalAlpha < 1.0) - destColor *= 1.0 / totalAlpha; + if (totalOpacity >= 0.0 && totalOpacity < 1.0) + destColor *= (1.0 - (totalOpacity * 0.5)) / (1.0 - totalOpacity); - destColor.a = totalAlpha; + destColor.a = (1.0 - totalOpacity); gl_FragColor = clamp(destColor, 0.0, 1.0); } |