Feature request for all paint systems that support it: Jittering in

absolute coordinates. This allows an artist to lower the brush radius
while keeping the spread of the brush constant. A toggle under the
jitter slider provides the option to switch between relative/absolute.

release/scripts/startup/bl_ui/space_image.py

@@ -698,8 +698,13 @@ class IMAGE_PT_paint(Panel, ImagePaintPanel):
             self.prop_unified_strength(row, context, brush, "use_pressure_strength")
 
             row = col.row(align=True)
-            row.prop(brush, "jitter", slider=True)
+            if(brush.use_absolute_jitter):
+                row.prop(brush, "jitter_absolute", slider=True)
+            else:
+                row.prop(brush, "jitter", slider=True)
             row.prop(brush, "use_pressure_jitter", toggle=True, text="")
+            
+            col.prop(brush, "use_absolute_jitter")
 
             col.prop(brush, "blend", text="Blend")
 

release/scripts/startup/bl_ui/space_view3d_toolbar.py

@@ -678,8 +678,13 @@ class VIEW3D_PT_tools_brush(Panel, View3DPaintPanel):
             self.prop_unified_strength(row, context, brush, "use_pressure_strength")
 
             row = col.row(align=True)
-            row.prop(brush, "jitter", slider=True)
+            if(brush.use_absolute_jitter):
+                row.prop(brush, "jitter_absolute")
+            else:
+                row.prop(brush, "jitter", slider=True)
             row.prop(brush, "use_pressure_jitter", toggle=True, text="")
+           
+            col.prop(brush, "use_absolute_jitter")
 
             col.prop(brush, "blend", text="Blend")
 
@@ -706,8 +711,13 @@ class VIEW3D_PT_tools_brush(Panel, View3DPaintPanel):
             self.prop_unified_strength(row, context, brush, "use_pressure_strength")
 
             row = col.row(align=True)
-            row.prop(brush, "jitter", slider=True)
+            if(brush.use_absolute_jitter):
+                row.prop(brush, "jitter_absolute")
+            else:
+                row.prop(brush, "jitter", slider=True)
             row.prop(brush, "use_pressure_jitter", toggle=True, text="")
+            
+            col.prop(brush, "use_absolute_jitter")
 
             col.prop(brush, "vertex_tool", text="Blend")
 
@@ -828,8 +838,13 @@ class VIEW3D_PT_tools_brush_stroke(Panel, View3DPaintPanel):
                 col.separator()
 
                 row = col.row(align=True)
-                row.prop(brush, "jitter", slider=True)
+                if(brush.use_absolute_jitter):
+                    row.prop(brush, "jitter_absolute")
+                else:
+                    row.prop(brush, "jitter", slider=True)
                 row.prop(brush, "use_pressure_jitter", toggle=True, text="")
+          
+                col.prop(brush, "use_absolute_jitter")
 
         else:
             col.prop(brush, "use_airbrush")

source/blender/blenkernel/intern/brush.c

@@ -791,7 +791,8 @@ void BKE_brush_scale_size(int *r_brush_size,
 
 void BKE_brush_jitter_pos(const Scene *scene, Brush *brush, const float pos[2], float jitterpos[2])
 {
-	int use_jitter = brush->jitter != 0;
+	int use_jitter = (brush->flag & BRUSH_ABSOLUTE_JITTER) ?
+		(brush->jitter_absolute != 0) : (brush->jitter != 0);
 
 	/* jitter-ed brush gives weird and unpredictable result for this
 	 * kinds of stroke, so manually disable jitter usage (sergey) */
@@ -799,17 +800,26 @@ void BKE_brush_jitter_pos(const Scene *scene, Brush *brush, const float pos[2],
 
 	if (use_jitter) {
 		float rand_pos[2];
-		const int radius = BKE_brush_size_get(scene, brush);
-		const int diameter = 2 * radius;
+		float spread;
+		int diameter;
 
-		/* find random position within a circle of diameter 1 */
 		do {
 			rand_pos[0] = BLI_frand() - 0.5f;
 			rand_pos[1] = BLI_frand() - 0.5f;
 		} while (len_v2(rand_pos) > 0.5f);
 
-		jitterpos[0] = pos[0] + 2 * rand_pos[0] * diameter * brush->jitter;
-		jitterpos[1] = pos[1] + 2 * rand_pos[1] * diameter * brush->jitter;
+
+		if (brush->flag & BRUSH_ABSOLUTE_JITTER) {
+			diameter = 2 * brush->jitter_absolute;
+			spread = 1.0;
+		}
+		else {
+			diameter = 2 * BKE_brush_size_get(scene, brush);
+			spread = brush->jitter;
+		}
+		/* find random position within a circle of diameter 1 */
+		jitterpos[0] = pos[0] + 2 * rand_pos[0] * diameter * spread;
+		jitterpos[1] = pos[1] + 2 * rand_pos[1] * diameter * spread;
 	}
 	else {
 		copy_v2_v2(jitterpos, pos);

source/blender/editors/sculpt_paint/paint_stroke.c

@@ -169,6 +169,10 @@ static void paint_brush_stroke_add_step(bContext *C, wmOperator *op, wmEvent *ev
 		return;
 #endif
 
+	/* copy last position -before- jittering, or space fill code
+	 * will create too many dabs */
+	copy_v2_v2(stroke->last_mouse_position, mouse_in);
+
 	/* TODO: as sculpt and other paint modes are unified, this
 	 * separation will go away */
 	if (paint_supports_jitter(mode)) {
@@ -203,8 +207,6 @@ static void paint_brush_stroke_add_step(bContext *C, wmOperator *op, wmEvent *ev
 	RNA_boolean_set(&itemptr, "pen_flip", pen_flip);
 	RNA_float_set(&itemptr, "pressure", pressure);
 
-	copy_v2_v2(stroke->last_mouse_position, mouse_out);
-
 	stroke->update_step(C, stroke, &itemptr);
 }
 

source/blender/makesdna/DNA_brush_types.h

@@ -71,6 +71,8 @@ typedef struct Brush {
 	int size;           /* brush diameter */
 	int flag;           /* general purpose flag */
 	float jitter;       /* jitter the position of the brush */
+	int jitter_absolute;	/* absolute jitter in pixels */
+	int pad;
 	int spacing;        /* spacing of paint operations */
 	int smooth_stroke_radius;   /* turning radius (in pixels) for smooth stroke */
 	float smooth_stroke_factor; /* higher values limit fast changes in the stroke direction */
@@ -137,7 +139,8 @@ typedef enum BrushFlags {
 
 	/* temporary flag which sets up automatically for correct brush
 	 * drawing when inverted modal operator is running */
-	BRUSH_INVERTED = (1 << 29)
+	BRUSH_INVERTED = (1 << 29),
+	BRUSH_ABSOLUTE_JITTER = (1 << 30)
 } BrushFlags;
 
 /* Brush.sculpt_tool */

source/blender/makesrna/intern/rna_brush.c

@@ -637,6 +637,12 @@ static void rna_def_brush(BlenderRNA *brna)
 	RNA_def_property_ui_text(prop, "Jitter", "Jitter the position of the brush while painting");
 	RNA_def_property_update(prop, 0, "rna_Brush_update");
 
+	prop = RNA_def_property(srna, "jitter_absolute", PROP_INT, PROP_NONE);
+	RNA_def_property_int_sdna(prop, NULL, "jitter_absolute");
+	RNA_def_property_range(prop, 0, 1000000);
+	RNA_def_property_ui_text(prop, "Absolute Jitter", "Jitter the position of the brush while painting in pixels");
+	RNA_def_property_update(prop, 0, "rna_Brush_update");
+
 	prop = RNA_def_property(srna, "spacing", PROP_INT, PROP_PERCENTAGE);
 	RNA_def_property_int_sdna(prop, NULL, "spacing");
 	RNA_def_property_range(prop, 1, 1000);
@@ -793,6 +799,11 @@ static void rna_def_brush(BlenderRNA *brna)
 	RNA_def_property_ui_text(prop, "Rake", "Rotate the brush texture to match the stroke direction");
 	RNA_def_property_update(prop, 0, "rna_Brush_update");
 
+	prop = RNA_def_property(srna, "use_absolute_jitter", PROP_BOOLEAN, PROP_NONE);
+	RNA_def_property_boolean_sdna(prop, NULL, "flag", BRUSH_ABSOLUTE_JITTER);
+	RNA_def_property_ui_text(prop, "Absolute Jitter", "Jittering happens in screen space, not relative to brush size");
+	RNA_def_property_update(prop, 0, "rna_Brush_update");
+
 	prop = RNA_def_property(srna, "use_random_rotation", PROP_BOOLEAN, PROP_NONE);
 	RNA_def_property_boolean_sdna(prop, NULL, "flag", BRUSH_RANDOM_ROTATION);
 	RNA_def_property_ui_text(prop, "Random Rotation", "Rotate the brush texture at random");