DwM: Armature: Add distance outline and wire drawing of envelope bones.

This is not complete, it does not implement 3D solid drawing of
envelope bones. 2D wire is hence always drawn for now.

Some notes:

I did not try to implement the 'capsule' approach suggested by @fclem, because:
  1. I spent enough time on this already, and finally got something working.
  2. I managed to get rid of geometry shader completely.
  3. Current approach allows us to use same shader for
     distance outline and envelope wire.

It's working fine, except for one glitch - superpositions of envelope
outlines do not work as expected, not sure what's wrong here, tried to
disable zbuff, enable GL_BLEND, no luck so far...
I think we need our own 'background' drawpass to get them working (also
to avoid them drawing over the wire lines).

1 files changed, 111 insertions, 0 deletions

diff --git a/source/blender/draw/intern/draw_cache.c b/source/blender/draw/intern/draw_cache.c
index 36f95afc7f4..5b9247c1024 100644
--- a/source/blender/draw/intern/draw_cache.c
+++ b/source/blender/draw/intern/draw_cache.c
@@ -70,6 +70,9 @@ static struct DRWShapeCache {
 	Batch *drw_bone_box;
 	Batch *drw_bone_box_wire;
 	Batch *drw_bone_wire_wire;
+	Batch *drw_bone_envelope_distance;
+	Batch *drw_bone_envelope_wire;
+	Batch *drw_bone_envelope_head_wire;
 	Batch *drw_bone_point;
 	Batch *drw_bone_point_wire;
 	Batch *drw_bone_arrows;
@@ -110,6 +113,9 @@ void DRW_shape_cache_free(void)
 	BATCH_DISCARD_ALL_SAFE(SHC.drw_bone_box);
 	BATCH_DISCARD_ALL_SAFE(SHC.drw_bone_box_wire);
 	BATCH_DISCARD_ALL_SAFE(SHC.drw_bone_wire_wire);
+	BATCH_DISCARD_ALL_SAFE(SHC.drw_bone_envelope_distance);
+	BATCH_DISCARD_ALL_SAFE(SHC.drw_bone_envelope_wire);
+	BATCH_DISCARD_ALL_SAFE(SHC.drw_bone_envelope_head_wire);
 	BATCH_DISCARD_ALL_SAFE(SHC.drw_bone_point);
 	BATCH_DISCARD_ALL_SAFE(SHC.drw_bone_point_wire);
 	BATCH_DISCARD_ALL_SAFE(SHC.drw_bone_arrows);
@@ -1524,6 +1530,111 @@ Batch *DRW_cache_bone_wire_wire_outline_get(void)
 }
 
 
+Batch *DRW_cache_bone_envelope_distance_outline_get(void)
+{
+#define CIRCLE_RESOL 32
+	if (!SHC.drw_bone_envelope_distance) {
+		unsigned int v_idx = 0;
+
+		static VertexFormat format = { 0 };
+		static unsigned int pos_id;
+		if (format.attrib_ct == 0) {
+			pos_id = VertexFormat_add_attrib(&format, "pos", COMP_F32, 4, KEEP_FLOAT);
+		}
+
+		/* Vertices */
+		VertexBuffer *vbo = VertexBuffer_create_with_format(&format);
+		VertexBuffer_allocate_data(vbo, CIRCLE_RESOL * 2 + 6);
+
+		/* Encoded triangle strip, vertex shader gives them final correct value. */
+		for (int i = 0; i < CIRCLE_RESOL + 1; i++) {
+			const bool is_headtail_transition = ELEM(i, CIRCLE_RESOL / 2, CIRCLE_RESOL);
+			const float head_tail = (i > CIRCLE_RESOL / 2) ? 1.0f : 0.0f;
+			const float alpha = 2.0f * M_PI * i / CIRCLE_RESOL;
+			const float x = cosf(alpha);
+			const float y = -sinf(alpha);
+
+			/*                                                           { X, Y, head/tail, inner/outer border } */
+			VertexBuffer_set_attrib(vbo, pos_id, v_idx++, (const float[4]){x, y, head_tail, 0.0f});
+			VertexBuffer_set_attrib(vbo, pos_id, v_idx++, (const float[4]){x, y, head_tail, 1.0f});
+			if (is_headtail_transition) {
+				VertexBuffer_set_attrib(vbo, pos_id, v_idx++, (const float[4]){x, y, 1.0f - head_tail, 0.0f});
+				VertexBuffer_set_attrib(vbo, pos_id, v_idx++, (const float[4]){x, y, 1.0f - head_tail, 1.0f});
+			}
+		}
+
+		SHC.drw_bone_envelope_distance = Batch_create(PRIM_TRIANGLE_STRIP, vbo, NULL);
+	}
+	return SHC.drw_bone_envelope_distance;
+#undef CIRCLE_RESOL
+}
+
+
+/* Bone body and tail. */
+Batch *DRW_cache_bone_envelope_wire_outline_get(void)
+{
+	if (!SHC.drw_bone_envelope_wire) {
+		unsigned int v_idx = 0;
+
+		static VertexFormat format = { 0 };
+		static unsigned int pos_id;
+		if (format.attrib_ct == 0) {
+			pos_id = VertexFormat_add_attrib(&format, "pos", COMP_F32, 4, KEEP_FLOAT);
+		}
+
+		/* Vertices */
+		VertexBuffer *vbo = VertexBuffer_create_with_format(&format);
+		VertexBuffer_allocate_data(vbo, 4);
+
+		/* Two lines between head and tail circles. */
+		/* Encoded lines, vertex shader gives them final correct value. */
+		/*                                                           {     X,    Y, head/tail, inner/outer border } */
+		VertexBuffer_set_attrib(vbo, pos_id, v_idx++, (const float[4]){ 1.0f, 0.0f,       0.0f, 0.0f});
+		VertexBuffer_set_attrib(vbo, pos_id, v_idx++, (const float[4]){ 1.0f, 0.0f,       1.0f, 0.0f});
+		VertexBuffer_set_attrib(vbo, pos_id, v_idx++, (const float[4]){-1.0f, 0.0f,       0.0f, 0.0f});
+		VertexBuffer_set_attrib(vbo, pos_id, v_idx++, (const float[4]){-1.0f, 0.0f,       1.0f, 0.0f});
+
+		SHC.drw_bone_envelope_wire = Batch_create(PRIM_LINES, vbo, NULL);
+	}
+	return SHC.drw_bone_envelope_wire;
+}
+
+
+/* Bone head. */
+Batch *DRW_cache_bone_envelope_head_wire_outline_get(void)
+{
+#define CIRCLE_RESOL 32
+	if (!SHC.drw_bone_envelope_head_wire) {
+		unsigned int v_idx = 0;
+
+		static VertexFormat format = { 0 };
+		static unsigned int pos_id;
+		if (format.attrib_ct == 0) {
+			pos_id = VertexFormat_add_attrib(&format, "pos", COMP_F32, 4, KEEP_FLOAT);
+		}
+
+		/* Vertices */
+		VertexBuffer *vbo = VertexBuffer_create_with_format(&format);
+		VertexBuffer_allocate_data(vbo, CIRCLE_RESOL);
+
+		/* Encoded lines, vertex shader gives them final correct value. */
+		/* Only head circle (tail is drawn in disp_tail_mat space as a head one by draw_armature.c's draw_point()). */
+		for (int i = 0; i < CIRCLE_RESOL; i++) {
+			const float alpha = 2.0f * M_PI * i / CIRCLE_RESOL;
+			const float x = cosf(alpha);
+			const float y = -sinf(alpha);
+
+			/*                                                           {      X,      Y, head/tail, inner/outer border } */
+			VertexBuffer_set_attrib(vbo, pos_id, v_idx++, (const float[4]){     x,      y,      0.0f, 0.0f});
+		}
+
+		SHC.drw_bone_envelope_head_wire = Batch_create(PRIM_LINE_LOOP, vbo, NULL);
+	}
+	return SHC.drw_bone_envelope_head_wire;
+#undef CIRCLE_RESOL
+}
+
+
 Batch *DRW_cache_bone_point_get(void)
 {
 	if (!SHC.drw_bone_point) {