Smoke: Port display to Workbench + object mode

This does not fix the smokesim. It only port the drawing method.

The Object mode engine is in charge of rendering the velocity debugging.

Things left to do:
- Flame rendering.
- Color Ramp coloring of volume data.
- View facing slicing (for now it's only doing sampling starting from the
  volume bounds which gives a squarish look)
- Add option to enable dithering (currently on by default.

4 files changed, 80 insertions, 3 deletions

diff --git a/source/blender/draw/intern/draw_cache.c b/source/blender/draw/intern/draw_cache.c
index 1bf40673239..0d2317199fc 100644
--- a/source/blender/draw/intern/draw_cache.c
+++ b/source/blender/draw/intern/draw_cache.c
@@ -61,6 +61,7 @@ static struct DRWShapeCache {
 	Gwn_Batch *drw_square;
 	Gwn_Batch *drw_line;
 	Gwn_Batch *drw_line_endpoints;
+	Gwn_Batch *drw_empty_cube;
 	Gwn_Batch *drw_empty_sphere;
 	Gwn_Batch *drw_empty_cone;
 	Gwn_Batch *drw_arrows;
@@ -341,6 +342,54 @@ Gwn_Batch *DRW_cache_cube_get(void)
 			{ 1.0f,  1.0f,  1.0f}
 		};
 
+		const uint indices[36] = {
+			0, 1, 2,
+			1, 3, 2,
+			0, 4, 1,
+			4, 5, 1,
+			6, 5, 4,
+			6, 7, 5,
+			2, 7, 6,
+			2, 3, 7,
+			3, 1, 7,
+			1, 5, 7,
+			0, 2, 4,
+			2, 6, 4,
+		};
+
+		/* Position Only 3D format */
+		static Gwn_VertFormat format = { 0 };
+		static struct { uint pos; } attr_id;
+		if (format.attr_len == 0) {
+			attr_id.pos = GWN_vertformat_attr_add(&format, "pos", GWN_COMP_F32, 3, GWN_FETCH_FLOAT);
+		}
+
+		Gwn_VertBuf *vbo = GWN_vertbuf_create_with_format(&format);
+		GWN_vertbuf_data_alloc(vbo, 36);
+
+		for (int i = 0; i < 36; ++i) {
+			GWN_vertbuf_attr_set(vbo, attr_id.pos, i, verts[indices[i]]);
+		}
+
+		SHC.drw_cube = GWN_batch_create_ex(GWN_PRIM_TRIS, vbo, NULL, GWN_BATCH_OWNS_VBO);
+	}
+	return SHC.drw_cube;
+}
+
+Gwn_Batch *DRW_cache_empty_cube_get(void)
+{
+	if (!SHC.drw_empty_cube) {
+		const GLfloat verts[8][3] = {
+			{-1.0f, -1.0f, -1.0f},
+			{-1.0f, -1.0f,  1.0f},
+			{-1.0f,  1.0f, -1.0f},
+			{-1.0f,  1.0f,  1.0f},
+			{ 1.0f, -1.0f, -1.0f},
+			{ 1.0f, -1.0f,  1.0f},
+			{ 1.0f,  1.0f, -1.0f},
+			{ 1.0f,  1.0f,  1.0f}
+		};
+
 		const GLubyte indices[24] = {0, 1, 1, 3, 3, 2, 2, 0, 0, 4, 4, 5, 5, 7, 7, 6, 6, 4, 1, 5, 3, 7, 2, 6};
 
 		/* Position Only 3D format */
@@ -357,9 +406,9 @@ Gwn_Batch *DRW_cache_cube_get(void)
 			GWN_vertbuf_attr_set(vbo, attr_id.pos, i, verts[indices[i]]);
 		}
 
-		SHC.drw_cube = GWN_batch_create_ex(GWN_PRIM_LINES, vbo, NULL, GWN_BATCH_OWNS_VBO);
+		SHC.drw_empty_cube = GWN_batch_create_ex(GWN_PRIM_LINES, vbo, NULL, GWN_BATCH_OWNS_VBO);
 	}
-	return SHC.drw_cube;
+	return SHC.drw_empty_cube;
 }
 
 Gwn_Batch *DRW_cache_circle_get(void)
diff --git a/source/blender/draw/intern/draw_cache.h b/source/blender/draw/intern/draw_cache.h
index e7ab847d42e..9114a4d872d 100644
--- a/source/blender/draw/intern/draw_cache.h
+++ b/source/blender/draw/intern/draw_cache.h
@@ -41,6 +41,7 @@ struct Gwn_Batch *DRW_cache_cursor_get(bool crosshair_lines);
 /* Common Shapes */
 struct Gwn_Batch *DRW_cache_fullscreen_quad_get(void);
 struct Gwn_Batch *DRW_cache_quad_get(void);
+struct Gwn_Batch *DRW_cache_cube_get(void);
 struct Gwn_Batch *DRW_cache_sphere_get(void);
 struct Gwn_Batch *DRW_cache_single_vert_get(void);
 struct Gwn_Batch *DRW_cache_single_line_get(void);
@@ -61,7 +62,7 @@ void DRW_cache_object_face_wireframe_get(
 /* Empties */
 struct Gwn_Batch *DRW_cache_plain_axes_get(void);
 struct Gwn_Batch *DRW_cache_single_arrow_get(void);
-struct Gwn_Batch *DRW_cache_cube_get(void);
+struct Gwn_Batch *DRW_cache_empty_cube_get(void);
 struct Gwn_Batch *DRW_cache_circle_get(void);
 struct Gwn_Batch *DRW_cache_square_get(void);
 struct Gwn_Batch *DRW_cache_empty_sphere_get(void);
diff --git a/source/blender/draw/intern/draw_common.c b/source/blender/draw/intern/draw_common.c
index a1c60be4742..df80300417e 100644
--- a/source/blender/draw/intern/draw_common.c
+++ b/source/blender/draw/intern/draw_common.c
@@ -162,6 +162,8 @@ extern char datatoc_animviz_mpath_lines_vert_glsl[];
 extern char datatoc_animviz_mpath_lines_geom_glsl[];
 extern char datatoc_animviz_mpath_points_vert_glsl[];
 
+extern char datatoc_volume_velocity_vert_glsl[];
+
 extern char datatoc_armature_axes_vert_glsl[];
 extern char datatoc_armature_sphere_solid_vert_glsl[];
 extern char datatoc_armature_sphere_solid_frag_glsl[];
@@ -199,6 +201,9 @@ static struct {
 	struct GPUShader *mpath_line_sh;
 	struct GPUShader *mpath_points_sh;
 
+	struct GPUShader *volume_velocity_needle_sh;
+	struct GPUShader *volume_velocity_sh;
+
 	struct GPUShader *mball_handles;
 } g_shaders = {NULL};
 
@@ -736,6 +741,26 @@ struct GPUShader *mpath_points_shader_get(void)
 	return g_shaders.mpath_points_sh;
 }
 
+struct GPUShader *volume_velocity_shader_get(bool use_needle)
+{
+	if (use_needle) {
+		if (g_shaders.volume_velocity_needle_sh == NULL) {
+			g_shaders.volume_velocity_needle_sh = DRW_shader_create(
+			        datatoc_volume_velocity_vert_glsl, NULL,
+			        datatoc_gpu_shader_flat_color_frag_glsl, "#define USE_NEEDLE");
+		}
+		return g_shaders.volume_velocity_needle_sh;
+	}
+	else {
+		if (g_shaders.volume_velocity_sh == NULL) {
+			g_shaders.volume_velocity_sh = DRW_shader_create(
+			        datatoc_volume_velocity_vert_glsl, NULL,
+			        datatoc_gpu_shader_flat_color_frag_glsl, NULL);
+		}
+		return g_shaders.volume_velocity_sh;
+	}
+}
+
 /* ******************************************** COLOR UTILS *********************************************** */
 
 /* TODO FINISH */
diff --git a/source/blender/draw/intern/draw_common.h b/source/blender/draw/intern/draw_common.h
index 6227130fb05..b4ae0600f02 100644
--- a/source/blender/draw/intern/draw_common.h
+++ b/source/blender/draw/intern/draw_common.h
@@ -138,6 +138,8 @@ struct DRWShadingGroup *shgroup_instance_bone_stick(struct DRWPass *pass);
 struct GPUShader *mpath_line_shader_get(void);
 struct GPUShader *mpath_points_shader_get(void);
 
+struct GPUShader *volume_velocity_shader_get(bool use_needle);
+
 int DRW_object_wire_theme_get(
         struct Object *ob, struct ViewLayer *view_layer, float **r_color);
 float *DRW_color_background_blend_get(int theme_id);