Implement a new dedicated weight painting shader.

Move the weight paint drawing to the fragment shader. The shader
uses a texture that uses the U.coba_weight custom color band, or
an internal color band.

In addition to actual weights, the shader has to display two
alert colors: missing vertex group, and zero weight. The zero
weight alert has to be blended with regular weight colors,
so that a single alert vertex surrounded by weighted ones is
still visible.

Reviewers: campbellbarton, fclem

Differential Revision: https://developer.blender.org/D3675

9 files changed, 147 insertions, 82 deletions

diff --git a/source/blender/draw/CMakeLists.txt b/source/blender/draw/CMakeLists.txt
index f2a8256489d..06752e41092 100644
--- a/source/blender/draw/CMakeLists.txt
+++ b/source/blender/draw/CMakeLists.txt
@@ -307,6 +307,8 @@ data_to_c_simple(modes/shaders/paint_texture_frag.glsl SRC)
 data_to_c_simple(modes/shaders/paint_texture_vert.glsl SRC)
 data_to_c_simple(modes/shaders/paint_vertex_frag.glsl SRC)
 data_to_c_simple(modes/shaders/paint_vertex_vert.glsl SRC)
+data_to_c_simple(modes/shaders/paint_weight_frag.glsl SRC)
+data_to_c_simple(modes/shaders/paint_weight_vert.glsl SRC)
 data_to_c_simple(modes/shaders/paint_wire_frag.glsl SRC)
 data_to_c_simple(modes/shaders/paint_wire_vert.glsl SRC)
 data_to_c_simple(modes/shaders/paint_vert_frag.glsl SRC)
diff --git a/source/blender/draw/intern/draw_cache_impl_mesh.c b/source/blender/draw/intern/draw_cache_impl_mesh.c
index 0e451fe12a6..6a324aa078f 100644
--- a/source/blender/draw/intern/draw_cache_impl_mesh.c
+++ b/source/blender/draw/intern/draw_cache_impl_mesh.c
@@ -201,7 +201,7 @@ typedef struct MeshRenderData {
 	int *loose_verts;
 
 	float (*poly_normals)[3];
-	float (*vert_weight_color)[3];
+	float (*vert_weight);
 	char (*vert_color)[3];
 	GPUPackedNormal *poly_normals_pack;
 	GPUPackedNormal *vert_normals_pack;
@@ -845,7 +845,7 @@ static void mesh_render_data_free(MeshRenderData *rdata)
 	MEM_SAFE_FREE(rdata->poly_normals);
 	MEM_SAFE_FREE(rdata->poly_normals_pack);
 	MEM_SAFE_FREE(rdata->vert_normals_pack);
-	MEM_SAFE_FREE(rdata->vert_weight_color);
+	MEM_SAFE_FREE(rdata->vert_weight);
 	MEM_SAFE_FREE(rdata->edge_select_bool);
 	MEM_SAFE_FREE(rdata->vert_color);
 
@@ -1068,58 +1068,7 @@ fallback:
 	}
 }
 
-/* TODO, move into shader? */
-static void rgb_from_weight(float r_rgb[3], const float weight)
-{
-	const float blend = ((weight / 2.0f) + 0.5f);
-
-	if (weight <= 0.25f) {    /* blue->cyan */
-		r_rgb[0] = 0.0f;
-		r_rgb[1] = blend * weight * 4.0f;
-		r_rgb[2] = blend;
-	}
-	else if (weight <= 0.50f) {  /* cyan->green */
-		r_rgb[0] = 0.0f;
-		r_rgb[1] = blend;
-		r_rgb[2] = blend * (1.0f - ((weight - 0.25f) * 4.0f));
-	}
-	else if (weight <= 0.75f) {  /* green->yellow */
-		r_rgb[0] = blend * ((weight - 0.50f) * 4.0f);
-		r_rgb[1] = blend;
-		r_rgb[2] = 0.0f;
-	}
-	else if (weight <= 1.0f) {  /* yellow->red */
-		r_rgb[0] = blend;
-		r_rgb[1] = blend * (1.0f - ((weight - 0.75f) * 4.0f));
-		r_rgb[2] = 0.0f;
-	}
-	else {
-		/* exceptional value, unclamped or nan,
-		 * avoid uninitialized memory use */
-		r_rgb[0] = 1.0f;
-		r_rgb[1] = 0.0f;
-		r_rgb[2] = 1.0f;
-	}
-}
-
-static void vertex_weight_color(float vweight[3], float weight, bool show_alert_color)
-{
-	CLAMP(weight, 0.0f, 1.0f);
-
-	if (show_alert_color) {
-		bTheme *theme = U.themes.first;
-
-		rgb_uchar_to_float(vweight, (uchar *)theme->tv3d.vertex_unreferenced);
-	}
-	else if (U.flag & USER_CUSTOM_RANGE) {
-		BKE_colorband_evaluate(&U.coba_weight, weight, vweight);
-	}
-	else {
-		rgb_from_weight(vweight, weight);
-	}
-}
-
-static void evaluate_vertex_weight(float vweight[3], const MDeformVert *dvert, const struct DRW_MeshWeightState *wstate)
+static float evaluate_vertex_weight(const MDeformVert *dvert, const struct DRW_MeshWeightState *wstate)
 {
 	float input = 0.0f;
 	bool show_alert_color = false;
@@ -1152,16 +1101,19 @@ static void evaluate_vertex_weight(float vweight[3], const MDeformVert *dvert, c
 		}
 	}
 
-	vertex_weight_color(vweight, input, show_alert_color);
+	if (show_alert_color) {
+		return -1.0f;
+	}
+	else {
+		CLAMP(input, 0.0f, 1.0f);
+		return input;
+	}
 }
 
-/* color-code for missing data (full brightness isn't easy on the eye). */
-static const unsigned char missing_weight_color[3] = { 0xa0, 0x00, 0xa0 };
-
-/** Ensure #MeshRenderData.vert_weight_color */
-static void mesh_render_data_ensure_vert_weight_color(MeshRenderData *rdata, const struct DRW_MeshWeightState *wstate)
+/** Ensure #MeshRenderData.vert_weight */
+static void mesh_render_data_ensure_vert_weight(MeshRenderData *rdata, const struct DRW_MeshWeightState *wstate)
 {
-	float (*vweight)[3] = rdata->vert_weight_color;
+	float (*vweight) = rdata->vert_weight;
 	if (vweight == NULL) {
 		if (wstate->defgroup_active == -1) {
 			goto fallback;
@@ -1178,10 +1130,10 @@ static void mesh_render_data_ensure_vert_weight_color(MeshRenderData *rdata, con
 			BMVert *eve;
 			int i;
 
-			vweight = rdata->vert_weight_color = MEM_mallocN(sizeof(*vweight) * rdata->vert_len, __func__);
+			vweight = rdata->vert_weight = MEM_mallocN(sizeof(*vweight) * rdata->vert_len, __func__);
 			BM_ITER_MESH_INDEX(eve, &viter, bm, BM_VERT, i) {
 				const MDeformVert *dvert = BM_ELEM_CD_GET_VOID_P(eve, cd_dvert_offset);
-				evaluate_vertex_weight(vweight[i], dvert, wstate);
+				vweight[i] = evaluate_vertex_weight(dvert, wstate);
 			}
 		}
 		else {
@@ -1189,31 +1141,26 @@ static void mesh_render_data_ensure_vert_weight_color(MeshRenderData *rdata, con
 				goto fallback;
 			}
 
-			vweight = rdata->vert_weight_color = MEM_mallocN(sizeof(*vweight) * rdata->vert_len, __func__);
+			vweight = rdata->vert_weight = MEM_mallocN(sizeof(*vweight) * rdata->vert_len, __func__);
 			for (int i = 0; i < rdata->vert_len; i++) {
-				evaluate_vertex_weight(vweight[i], &rdata->dvert[i], wstate);
+				vweight[i] = evaluate_vertex_weight(&rdata->dvert[i], wstate);
 			}
 		}
 	}
 	return;
 
 fallback:
-	vweight = rdata->vert_weight_color = MEM_mallocN(sizeof(*vweight) * rdata->vert_len, __func__);
-
-	float error_color[3];
+	vweight = rdata->vert_weight = MEM_callocN(sizeof(*vweight) * rdata->vert_len, __func__);
 
 	if ((wstate->defgroup_active < 0) && (wstate->defgroup_len > 0)) {
-		rgb_uchar_to_float(error_color, missing_weight_color);
+		copy_vn_fl(vweight, rdata->vert_len, -2.0f);
 	}
-	else {
-		vertex_weight_color(error_color, 0.0f, wstate->alert_mode != OB_DRAW_GROUPUSER_NONE);
-	}
-
-	for (int i = 0; i < rdata->vert_len; i++) {
-		copy_v3_v3(vweight[i], error_color);
+	else if (wstate->alert_mode != OB_DRAW_GROUPUSER_NONE) {
+		copy_vn_fl(vweight, rdata->vert_len, -1.0f);
 	}
 }
 
+
 /** Ensure #MeshRenderData.edge_select_bool */
 static void mesh_render_data_ensure_edge_select_bool(MeshRenderData *rdata, bool use_wire)
 {
@@ -2782,9 +2729,9 @@ static GPUVertBuf *mesh_create_tri_weights(
 		uint cidx = 0;
 
 		static GPUVertFormat format = { 0 };
-		static struct { uint col; } attr_id;
+		static struct { uint weight; } attr_id;
 		if (format.attr_len == 0) {
-			attr_id.col = GPU_vertformat_attr_add(&format, "color", GPU_COMP_F32, 3, GPU_FETCH_FLOAT);
+			attr_id.weight = GPU_vertformat_attr_add(&format, "weight", GPU_COMP_F32, 1, GPU_FETCH_FLOAT);
 		}
 
 		vbo = GPU_vertbuf_create_with_format(&format);
@@ -2794,8 +2741,8 @@ static GPUVertBuf *mesh_create_tri_weights(
 		int vbo_len_used = 0;
 		GPU_vertbuf_data_alloc(vbo, vbo_len_capacity);
 
-		mesh_render_data_ensure_vert_weight_color(rdata, wstate);
-		const float (*vert_weight_color)[3] = rdata->vert_weight_color;
+		mesh_render_data_ensure_vert_weight(rdata, wstate);
+		const float (*vert_weight) = rdata->vert_weight;
 
 		if (rdata->edit_bmesh) {
 			for (int i = 0; i < tri_len; i++) {
@@ -2804,7 +2751,7 @@ static GPUVertBuf *mesh_create_tri_weights(
 				if (!BM_elem_flag_test(ltri[0]->f, BM_ELEM_HIDDEN)) {
 					for (uint tri_corner = 0; tri_corner < 3; tri_corner++) {
 						const int v_index = BM_elem_index_get(ltri[tri_corner]->v);
-						GPU_vertbuf_attr_set(vbo, attr_id.col, cidx++, vert_weight_color[v_index]);
+						GPU_vertbuf_attr_set(vbo, attr_id.weight, cidx++, &vert_weight[v_index]);
 					}
 				}
 			}
@@ -2815,7 +2762,7 @@ static GPUVertBuf *mesh_create_tri_weights(
 				if (!(use_hide && (rdata->mpoly[mlt->poly].flag & ME_HIDE))) {
 					for (uint tri_corner = 0; tri_corner < 3; tri_corner++) {
 						const uint v_index = rdata->mloop[mlt->tri[tri_corner]].v;
-						GPU_vertbuf_attr_set(vbo, attr_id.col, cidx++, vert_weight_color[v_index]);
+						GPU_vertbuf_attr_set(vbo, attr_id.weight, cidx++, &vert_weight[v_index]);
 					}
 				}
 			}
diff --git a/source/blender/draw/intern/draw_common.c b/source/blender/draw/intern/draw_common.c
index eeaa204a252..faa4d980cd1 100644
--- a/source/blender/draw/intern/draw_common.c
+++ b/source/blender/draw/intern/draw_common.c
@@ -47,6 +47,12 @@
 GlobalsUboStorage ts;
 struct GPUUniformBuffer *globals_ubo = NULL;
 struct GPUTexture *globals_ramp = NULL;
+struct GPUTexture *globals_weight_ramp = NULL;
+
+static bool weight_ramp_custom = false;
+static ColorBand weight_ramp_copy;
+
+static struct GPUTexture* DRW_create_weight_colorramp_texture(void);
 
 void DRW_globals_update(void)
 {
@@ -63,6 +69,8 @@ void DRW_globals_update(void)
 	UI_GetThemeColor4fv(TH_EMPTY, ts.colorEmpty);
 	UI_GetThemeColor4fv(TH_VERTEX, ts.colorVertex);
 	UI_GetThemeColor4fv(TH_VERTEX_SELECT, ts.colorVertexSelect);
+	UI_GetThemeColor4fv(TH_VERTEX_UNREFERENCED, ts.colorVertexUnreferenced);
+	UI_COLOR_RGBA_FROM_U8(0xB0, 0x00, 0xB0, 0xFF, ts.colorVertexMissingData);
 	UI_GetThemeColor4fv(TH_EDITMESH_ACTIVE, ts.colorEditMeshActive);
 	UI_GetThemeColor4fv(TH_EDGE_SELECT, ts.colorEdgeSelect);
 
@@ -174,6 +182,21 @@ void DRW_globals_update(void)
 	globals_ramp = GPU_texture_create_1D(col_size, GPU_RGBA8, colors, NULL);
 
 	MEM_freeN(colors);
+
+	/* Weight Painting color ramp texture */
+	bool user_weight_ramp = (U.flag & USER_CUSTOM_RANGE) != 0;
+
+	if (weight_ramp_custom != user_weight_ramp ||
+	    (user_weight_ramp && memcmp(&weight_ramp_copy, &U.coba_weight, sizeof(ColorBand)) != 0)) {
+		DRW_TEXTURE_FREE_SAFE(globals_weight_ramp);
+	}
+
+	if (globals_weight_ramp == NULL) {
+		weight_ramp_custom = user_weight_ramp;
+		memcpy(&weight_ramp_copy, &U.coba_weight, sizeof(ColorBand));
+
+		globals_weight_ramp = DRW_create_weight_colorramp_texture();
+	}
 }
 
 /* ********************************* SHGROUP ************************************* */
@@ -924,3 +947,36 @@ bool DRW_object_axis_orthogonal_to_view(Object *ob, int axis)
 
 	return false;
 }
+
+static void DRW_evaluate_weight_to_color(float *result, float weight)
+{
+	if (U.flag & USER_CUSTOM_RANGE)
+	{
+		BKE_colorband_evaluate(&U.coba_weight, weight, result);
+	}
+	else {
+		/* Use gamma correction to even out the color bands:
+		 * increasing widens yellow/cyan vs red/green/blue.
+		 * Gamma 1.0 produces the original 2.79 color ramp. */
+		const float gamma = 1.5f;
+		float hsv[3] = { (2.0f / 3.0f) * (1.0f - weight), 1.0f, pow(0.5f + 0.5f * weight, gamma) };
+
+		hsv_to_rgb_v(hsv, result);
+
+		for (int i = 0; i < 3; i++) {
+			result[i] = pow(result[i], 1.0f/gamma);
+		}
+	}
+}
+
+static GPUTexture* DRW_create_weight_colorramp_texture(void)
+{
+	char error[256];
+	float pixels[256 * 4];
+	for (int i = 0 ; i < 256 ; i ++) {
+		DRW_evaluate_weight_to_color(&pixels[i*4], i / 255.0f);
+		pixels[i*4 + 3] = 1.0f;
+	}
+
+	return GPU_texture_create_1D(256, GPU_RGBA8, pixels, error);
+}
diff --git a/source/blender/draw/intern/draw_common.h b/source/blender/draw/intern/draw_common.h
index 2640451a889..a7de7fdeafa 100644
--- a/source/blender/draw/intern/draw_common.h
+++ b/source/blender/draw/intern/draw_common.h
@@ -57,6 +57,8 @@ typedef struct GlobalsUboStorage {
 	float colorEmpty[4];
 	float colorVertex[4];
 	float colorVertexSelect[4];
+	float colorVertexUnreferenced[4];
+	float colorVertexMissingData[4];
 	float colorEditMeshActive[4];
 	float colorEdgeSelect[4];
 	float colorEdgeSeam[4];
diff --git a/source/blender/draw/intern/draw_manager.c b/source/blender/draw/intern/draw_manager.c
index 41c905337ac..487e1d7a3ac 100644
--- a/source/blender/draw/intern/draw_manager.c
+++ b/source/blender/draw/intern/draw_manager.c
@@ -2528,6 +2528,7 @@ void DRW_engines_register(void)
 extern struct GPUVertFormat *g_pos_format; /* draw_shgroup.c */
 extern struct GPUUniformBuffer *globals_ubo; /* draw_common.c */
 extern struct GPUTexture *globals_ramp; /* draw_common.c */
+extern struct GPUTexture *globals_weight_ramp; /* draw_common.c */
 void DRW_engines_free(void)
 {
 	DRW_opengl_context_enable();
@@ -2553,6 +2554,7 @@ void DRW_engines_free(void)
 	DRW_UBO_FREE_SAFE(globals_ubo);
 	DRW_UBO_FREE_SAFE(view_ubo);
 	DRW_TEXTURE_FREE_SAFE(globals_ramp);
+	DRW_TEXTURE_FREE_SAFE(globals_weight_ramp);
 	MEM_SAFE_FREE(g_pos_format);
 
 	MEM_SAFE_FREE(DST.RST.bound_texs);
diff --git a/source/blender/draw/modes/paint_weight_mode.c b/source/blender/draw/modes/paint_weight_mode.c
index 68d1ffab2e6..f5394e4e925 100644
--- a/source/blender/draw/modes/paint_weight_mode.c
+++ b/source/blender/draw/modes/paint_weight_mode.c
@@ -43,6 +43,10 @@
 extern struct GPUUniformBuffer *globals_ubo; /* draw_common.c */
 extern struct GlobalsUboStorage ts; /* draw_common.c */
 
+extern struct GPUTexture *globals_weight_ramp; /* draw_common.c */
+
+extern char datatoc_paint_weight_vert_glsl[];
+extern char datatoc_paint_weight_frag_glsl[];
 extern char datatoc_paint_wire_vert_glsl[];
 extern char datatoc_paint_wire_frag_glsl[];
 extern char datatoc_paint_vert_frag_glsl[];
@@ -91,7 +95,10 @@ typedef struct PAINT_WEIGHT_PrivateData {
 static void PAINT_WEIGHT_engine_init(void *UNUSED(vedata))
 {
 	if (!e_data.weight_face_shader) {
-		e_data.weight_face_shader = GPU_shader_get_builtin_shader(GPU_SHADER_MULTIPLY_AND_BLEND_PREPROCESSING);
+		e_data.weight_face_shader = DRW_shader_create_with_lib(
+		        datatoc_paint_weight_vert_glsl, NULL,
+		        datatoc_paint_weight_frag_glsl,
+		        datatoc_common_globals_lib_glsl, NULL);
 	}
 
 	if (!e_data.wire_overlay_shader) {
@@ -134,6 +141,8 @@ static void PAINT_WEIGHT_cache_init(void *vedata)
 		stl->g_data->fweights_shgrp = DRW_shgroup_create(e_data.weight_face_shader, psl->weight_faces);
 
 		DRW_shgroup_uniform_float(stl->g_data->fweights_shgrp, "opacity", &v3d->overlay.weight_paint_mode_opacity, 1);
+		DRW_shgroup_uniform_texture(stl->g_data->fweights_shgrp, "colorramp", globals_weight_ramp);
+		DRW_shgroup_uniform_block(stl->g_data->fweights_shgrp, "globalsBlock", globals_ubo);
 	}
 
 	{
@@ -214,6 +223,7 @@ static void PAINT_WEIGHT_draw_scene(void *vedata)
 
 static void PAINT_WEIGHT_engine_free(void)
 {
+	DRW_SHADER_FREE_SAFE(e_data.weight_face_shader);
 	DRW_SHADER_FREE_SAFE(e_data.wire_overlay_shader);
 	DRW_SHADER_FREE_SAFE(e_data.vert_overlay_shader);
 }
diff --git a/source/blender/draw/modes/shaders/common_globals_lib.glsl b/source/blender/draw/modes/shaders/common_globals_lib.glsl
index bf761cd7c79..f1d118e572a 100644
--- a/source/blender/draw/modes/shaders/common_globals_lib.glsl
+++ b/source/blender/draw/modes/shaders/common_globals_lib.glsl
@@ -14,6 +14,8 @@ layout(std140) uniform globalsBlock {
 	vec4 colorEmpty;
 	vec4 colorVertex;
 	vec4 colorVertexSelect;
+	vec4 colorVertexUnreferenced;
+	vec4 colorVertexMissingData;
 	vec4 colorEditMeshActive;
 	vec4 colorEdgeSelect;
 	vec4 colorEdgeSeam;
diff --git a/source/blender/draw/modes/shaders/paint_weight_frag.glsl b/source/blender/draw/modes/shaders/paint_weight_frag.glsl
new file mode 100644
index 00000000000..668ca9e3c07
--- /dev/null
+++ b/source/blender/draw/modes/shaders/paint_weight_frag.glsl
@@ -0,0 +1,29 @@
+
+in vec2 weight_interp; /* (weight, alert) */
+
+out vec4 fragColor;
+
+uniform float opacity = 1.0;
+uniform sampler1D colorramp;
+
+void main()
+{
+	float alert = weight_interp.y;
+	vec4 color;
+
+	/* Missing vertex group alert color */
+	if (alert > 1.0) {
+		color = colorVertexMissingData;
+	}
+	/* Weights are available */
+	else {
+		float weight = weight_interp.x;
+		vec4 weight_color = texture(colorramp, weight, 0);
+
+		/* Zero weight alert color. Nonlinear blend to reduce impact. */
+		color = mix(weight_color, colorVertexUnreferenced, alert * alert);
+	}
+
+	/* See gpu_shader_multiply_and_blend_preprocessing.glsl */
+	fragColor = vec4(color.rgb * opacity + (1 - opacity), 1.0);
+}
diff --git a/source/blender/draw/modes/shaders/paint_weight_vert.glsl b/source/blender/draw/modes/shaders/paint_weight_vert.glsl
new file mode 100644
index 00000000000..78a3695c82c
--- /dev/null
+++ b/source/blender/draw/modes/shaders/paint_weight_vert.glsl
@@ -0,0 +1,15 @@
+
+uniform mat4 ModelViewProjectionMatrix;
+
+in float weight;
+in vec3 pos;
+
+out vec2 weight_interp; /* (weight, alert) */
+
+void main()
+{
+	gl_Position = ModelViewProjectionMatrix * vec4(pos, 1.0);
+
+	/* Separate actual weight and alerts for independent interpolation */
+	weight_interp = max(vec2(weight, -weight), 0.0);
+}