Object Mode: Grid: Add a non-hard depth test.

This adds a custom depth test that have the benefits to glitch less and be more visually pleasing.
Downside is that it let the grid pass trough the objects a little.

This effect is done in NDC space so that it counteract the logarithmic depth distribution imprecision (read as it's less visible near the camera but more present far away).

This patch also includes some cleanups.

source/blender/draw/modes/object_mode.c

@@ -224,7 +224,6 @@ static struct {
 	float camera_pos[3];
 	float screenvecs[3][4];
 	float grid_settings[5];
-	float grid_mat[4][4];
 	int grid_flag;
 	float grid_normal[3];
 	float grid_axes[3];
@@ -352,7 +351,7 @@ static void OBJECT_engine_init(void *vedata)
 		Scene *scene = draw_ctx->scene;
 		RegionView3D *rv3d = draw_ctx->rv3d;
 		float grid_scale = ED_view3d_grid_scale(scene, v3d, NULL);
-		float grid_res, offs;
+		float grid_res;
 
 		const bool show_axis_x = (v3d->gridflag & V3D_SHOW_X) != 0;
 		const bool show_axis_y = (v3d->gridflag & V3D_SHOW_Y) != 0;
@@ -385,10 +384,6 @@ static void OBJECT_engine_init(void *vedata)
 			fov = angle_v3v3(viewvecs[0], viewvecs[1]) / 2.0f;
 			grid_res = fabsf(tanf(fov)) / grid_scale;
 
-			/* Grid matrix polygon offset (fix depth fighting) */
-			/* see ED_view3d_polygon_offset */
-			offs = winmat[3][2] * -0.0025f;
-
 			e_data.grid_flag = (1 << 4); /* XY plane */
 			if (show_axis_x)
 				e_data.grid_flag |= SHOW_AXIS_X;
@@ -402,9 +397,6 @@ static void OBJECT_engine_init(void *vedata)
 			float viewdist = 1.0f / max_ff(fabsf(winmat[0][0]), fabsf(winmat[1][1]));
 			grid_res = viewdist / grid_scale;
 
-			/* Grid matrix polygon offset (fix depth fighting) */
-			/* see ED_view3d_polygon_offset */
-			offs = 0.00001f * viewdist;
 			if (ELEM(rv3d->view, RV3D_VIEW_RIGHT, RV3D_VIEW_LEFT)) {
 				e_data.grid_flag = PLANE_YZ;
 				e_data.grid_flag |= SHOW_AXIS_Y;
@@ -509,9 +501,6 @@ static void OBJECT_engine_init(void *vedata)
 			e_data.zneg_flag = e_data.zpos_flag = CLIP_ZNEG | CLIP_ZPOS;
 		}
 
-		winmat[3][2] -= offs;
-		mul_m4_m4m4(e_data.grid_mat, winmat, viewmat);
-
 		float dist = (rv3d->persp == RV3D_CAMOB && v3d->camera)
 		             ? ((Camera *)v3d->camera)->clipend : v3d->far;
 
@@ -796,7 +785,7 @@ static void OBJECT_cache_init(void *vedata)
 
 	{
 		/* Grid pass */
-		DRWState state = DRW_STATE_WRITE_COLOR | DRW_STATE_DEPTH_LESS | DRW_STATE_BLEND;
+		DRWState state = DRW_STATE_WRITE_COLOR | DRW_STATE_BLEND;
 		psl->grid = DRW_pass_create("Infinite Grid Pass", state);
 
 		struct Gwn_Batch *quad = DRW_cache_fullscreen_quad_get();
@@ -808,13 +797,13 @@ static void OBJECT_cache_init(void *vedata)
 		DRW_shgroup_uniform_int(grp, "gridFlag", &e_data.zneg_flag, 1);
 		DRW_shgroup_uniform_vec3(grp, "planeNormal", e_data.zplane_normal, 1);
 		DRW_shgroup_uniform_vec3(grp, "planeAxes", e_data.zplane_axes, 1);
-		DRW_shgroup_uniform_mat4(grp, "ViewProjectionOffsetMatrix", (float *)e_data.grid_mat);
 		DRW_shgroup_uniform_vec3(grp, "cameraPos", e_data.camera_pos, 1);
 		DRW_shgroup_uniform_vec4(grp, "screenvecs[0]", e_data.screenvecs[0], 3);
 		DRW_shgroup_uniform_vec4(grp, "gridSettings", e_data.grid_settings, 1);
 		DRW_shgroup_uniform_float(grp, "gridOneOverLogSubdiv", &e_data.grid_settings[4], 1);
 		DRW_shgroup_uniform_block(grp, "globalsBlock", globals_ubo);
 		DRW_shgroup_uniform_vec2(grp, "viewportSize", DRW_viewport_size_get(), 1);
+		DRW_shgroup_uniform_buffer(grp, "depthBuffer", &dtxl->depth);
 		DRW_shgroup_call_add(grp, quad, mat);
 
 		grp = DRW_shgroup_create(e_data.grid_sh, psl->grid);
@@ -822,6 +811,7 @@ static void OBJECT_cache_init(void *vedata)
 		DRW_shgroup_uniform_vec3(grp, "planeNormal", e_data.grid_normal, 1);
 		DRW_shgroup_uniform_vec3(grp, "planeAxes", e_data.grid_axes, 1);
 		DRW_shgroup_uniform_block(grp, "globalsBlock", globals_ubo);
+		DRW_shgroup_uniform_buffer(grp, "depthBuffer", &dtxl->depth);
 		DRW_shgroup_call_add(grp, quad, mat);
 
 		grp = DRW_shgroup_create(e_data.grid_sh, psl->grid);
@@ -829,6 +819,7 @@ static void OBJECT_cache_init(void *vedata)
 		DRW_shgroup_uniform_vec3(grp, "planeNormal", e_data.zplane_normal, 1);
 		DRW_shgroup_uniform_vec3(grp, "planeAxes", e_data.zplane_axes, 1);
 		DRW_shgroup_uniform_block(grp, "globalsBlock", globals_ubo);
+		DRW_shgroup_uniform_buffer(grp, "depthBuffer", &dtxl->depth);
 		DRW_shgroup_call_add(grp, quad, mat);
 	}
 
@@ -1887,6 +1878,8 @@ static void OBJECT_draw_scene(void *vedata)
 	OBJECT_StorageList *stl = ((OBJECT_Data *)vedata)->stl;
 	OBJECT_FramebufferList *fbl = ((OBJECT_Data *)vedata)->fbl;
 	DefaultFramebufferList *dfbl = DRW_viewport_framebuffer_list_get();
+	DefaultTextureList *dtxl = DRW_viewport_texture_list_get();
+
 	float clearcol[4] = {0.0f, 0.0f, 0.0f, 0.0f};
 
 	if (DRW_state_is_fbo()) {
@@ -1944,9 +1937,11 @@ static void OBJECT_draw_scene(void *vedata)
 
 	DRW_draw_pass(psl->ob_center);
 
-	if (!DRW_state_is_select()) {
+	if (DRW_state_is_fbo()) {
 		if (e_data.draw_grid) {
+			DRW_framebuffer_texture_detach(dtxl->depth);
 			DRW_draw_pass(psl->grid);
+			DRW_framebuffer_texture_attach(dfbl->default_fb, dtxl->depth, 0, 0);
 		}
 
 		/* Combine with scene buffer last */

source/blender/draw/modes/shaders/object_grid_frag.glsl

@@ -2,7 +2,6 @@
 /* Infinite grid
  * Clément Foucault */
 
-
 out vec4 FragColor;
 
 uniform mat4 ProjectionMatrix;
@@ -14,6 +13,7 @@ uniform vec4 gridSettings;
 uniform vec2 viewportSize;
 uniform vec4 screenvecs[3];
 uniform float gridOneOverLogSubdiv;
+uniform sampler2D depthBuffer;
 
 #define gridDistance      gridSettings.x
 #define gridResolution    gridSettings.y
@@ -120,6 +120,7 @@ void main()
 			angle = viewvec.z;
 
 		angle = 1.0 - abs(angle);
+		angle *= angle;
 		fade = 1.0 - angle * angle;
 		fade *= 1.0 - smoothstep(0.0, gridDistance, dist - gridDistance);
 	}
@@ -130,11 +131,24 @@ void main()
 
 		if ((gridFlag & PLANE_XY) > 0) {
 			float angle = 1.0 - abs(eye.z);
-			fade *= 1.0 - angle * angle * angle;
 			dist = 1.0 + angle * 2.0;
+			angle *= angle;
+			fade *= 1.0 - angle * angle;
 		}
 	}
 
+	/* Manual, non hard, depth test:
+	 * Progressively fade the grid below occluders
+	 * (avoids poping visuals due to depth buffer precision) */
+	float scene_depth = texture(depthBuffer, sPos).r;
+	/* Add a small bias so the grid will always
+	 * be on top of a mesh with the same depth. */
+	float grid_depth = gl_FragCoord.z - 1e-8;
+	/* Harder settings tend to flicker more,
+	 * but have less "see through" appearance. */
+	const float test_hardness = 1e4;
+	fade *= 1.0 - clamp((grid_depth - scene_depth) * test_hardness, 0.0, 1.0);
+
 	if ((gridFlag & GRID) > 0) {
 		float grid_res = log(dist * gridResolution) * gridOneOverLogSubdiv;
 

source/blender/draw/modes/shaders/object_grid_vert.glsl

@@ -2,7 +2,7 @@
 /* Infinite grid
  * Clément Foucault */
 
-uniform mat4 ViewProjectionOffsetMatrix;
+uniform mat4 ViewProjectionMatrix;
 uniform mat4 ProjectionMatrix;
 uniform vec3 cameraPos;
 uniform vec4 gridSettings;
@@ -59,5 +59,5 @@ void main()
 		realPos.z = min(-realPos.z, 0.0);
 	}
 
-	gl_Position = ViewProjectionOffsetMatrix * vec4(realPos, 1.0);
+	gl_Position = ViewProjectionMatrix * vec4(realPos, 1.0);
 }