Viewport smoke: add support for axis aligned slicing.

Current approach uses view aligned slicing to generate polygons for GL
texturing such that the generated polygons are always facing the view
plane. Now it is also possible to use object aligned slicing, which
creates polygons by slicing the object perpendicular to whichever axis
is facing the most the view plane. It is also possible to create a
single slice for inspecting the volume, or for 2D rendering effects.

Settings for this, along with a density multiplier setting, are to be
found in a newly added "Smoke Display Settings" panel in the smoke
domain properties tab.

Reviewers: plasmasolutions, gottfried

Differential Revision: https://developer.blender.org/D1733

1 files changed, 92 insertions, 3 deletions

diff --git a/source/blender/editors/space_view3d/drawvolume.c b/source/blender/editors/space_view3d/drawvolume.c
index 06677ef4476..d743e7c09e7 100644
--- a/source/blender/editors/space_view3d/drawvolume.c
+++ b/source/blender/editors/space_view3d/drawvolume.c
@@ -113,6 +113,63 @@ typedef struct VolumeSlicer {
 	float (*verts)[3];
 } VolumeSlicer;
 
+/* *************************** Axis Aligned Slicing ************************** */
+
+static void create_single_slice(VolumeSlicer *slicer, const float depth,
+                                const int axis, const int idx)
+{
+	const float vertices[3][4][3] = {
+	    {
+	        { depth, slicer->min[1], slicer->min[2] },
+	        { depth, slicer->max[1], slicer->min[2] },
+	        { depth, slicer->max[1], slicer->max[2] },
+	        { depth, slicer->min[1], slicer->max[2] }
+	    },
+	    {
+	        { slicer->min[0], depth, slicer->min[2] },
+	        { slicer->min[0], depth, slicer->max[2] },
+	        { slicer->max[0], depth, slicer->max[2] },
+	        { slicer->max[0], depth, slicer->min[2] }
+	    },
+	    {
+	        { slicer->min[0], slicer->min[1], depth },
+	        { slicer->min[0], slicer->max[1], depth },
+	        { slicer->max[0], slicer->max[1], depth },
+	        { slicer->max[0], slicer->min[1], depth }
+	    }
+	};
+
+	copy_v3_v3(slicer->verts[idx + 0], vertices[axis][0]);
+	copy_v3_v3(slicer->verts[idx + 1], vertices[axis][1]);
+	copy_v3_v3(slicer->verts[idx + 2], vertices[axis][2]);
+	copy_v3_v3(slicer->verts[idx + 3], vertices[axis][0]);
+	copy_v3_v3(slicer->verts[idx + 4], vertices[axis][2]);
+	copy_v3_v3(slicer->verts[idx + 5], vertices[axis][3]);
+}
+
+static void create_axis_aligned_slices(VolumeSlicer *slicer, const int num_slices,
+                                       const float view_dir[3], const int axis)
+{
+	float depth, slice_size = slicer->size[axis] / num_slices;
+
+	/* always process slices in back to front order! */
+	if (view_dir[axis] > 0.0f) {
+		depth = slicer->min[axis];
+	}
+	else {
+		depth = slicer->max[axis];
+		slice_size = -slice_size;
+	}
+
+	int count = 0;
+	for (int slice = 0; slice < num_slices; slice++) {
+		create_single_slice(slicer, depth, axis, count);
+
+		count += 6;
+		depth += slice_size;
+	}
+}
+
 /* *************************** View Aligned Slicing ************************** */
 
 /* Code adapted from:
@@ -433,8 +490,25 @@ void draw_smoke_volume(SmokeDomainSettings *sds, Object *ob,
 
 	/* setup slicing information */
 
-	const int max_slices = 256;
-	const int max_points = max_slices * 12;
+	const bool view_aligned = (sds->slice_method == MOD_SMOKE_SLICE_VIEW_ALIGNED);
+	int max_slices, max_points, axis = 0;
+
+	if (view_aligned) {
+		max_slices = max_iii(sds->res[0], sds->res[1], sds->res[2]) * sds->slice_per_voxel;
+		max_points = max_slices * 12;
+	}
+	else {
+		if (sds->axis_slice_method == AXIS_SLICE_FULL) {
+			axis = axis_dominant_v3_single(viewnormal);
+			max_slices = sds->res[axis] * sds->slice_per_voxel;
+		}
+		else {
+			axis = (sds->slice_axis == SLICE_AXIS_AUTO) ? axis_dominant_v3_single(viewnormal) : sds->slice_axis - 1;
+			max_slices = 1;
+		}
+
+		max_points = max_slices * 6;
+	}
 
 	VolumeSlicer slicer;
 	copy_v3_v3(slicer.min, min);
@@ -442,7 +516,22 @@ void draw_smoke_volume(SmokeDomainSettings *sds, Object *ob,
 	copy_v3_v3(slicer.size, size);
 	slicer.verts = MEM_mallocN(sizeof(float) * 3 * max_points, "smoke_slice_vertices");
 
-	const int num_points = create_view_aligned_slices(&slicer, max_slices, viewnormal);
+	int num_points;
+
+	if (view_aligned) {
+		num_points = create_view_aligned_slices(&slicer, max_slices, viewnormal);
+	}
+	else {
+		num_points = max_points;
+
+		if (sds->axis_slice_method == AXIS_SLICE_FULL) {
+			create_axis_aligned_slices(&slicer, max_slices, viewnormal, axis);
+		}
+		else {
+			const float depth = (sds->slice_depth - 0.5f) * size[axis];
+			create_single_slice(&slicer, depth, axis, 0);
+		}
+	}
 
 	/* setup buffer and draw */