Isosurface issues with depth

[martinfalk]

When rendering isosurfaces on top of geometry, e.g. a sphere mesh, there are some artifacts.

• holes when isosurface of the current ray segment lies behind the geometry (most likely caused by drawBackground() in raycastgeometry.glsl)
• a fully transparent isosurface is still writing depth

surface holes

---

depth of transparent isosurface

[r-englund]

issue is depth here:

inviwo/modules/opengl/glsl/utils/isosurface.glsl

Lines 119 to 122 in 975b66f

	if (tDepth < 0.0) {
	// store depth of first hit, i.e. voxel with non-zero alpha
	tDepth = t - tIncr;
	}