Basic pressure sensitivity support in imagepaint, for opacity, size,

falloff and spacing. Click the button labeled "P" next to the sliders.
Works best for opacity, other options can give poor quality strokes in
some cases. Also performance needs to be improved.

Remember, works only on X11 and Mac, no Windows support for tablets yet.

2 files changed, 55 insertions, 13 deletions

diff --git a/source/blender/blenkernel/BKE_brush.h b/source/blender/blenkernel/BKE_brush.h
index 52f86ef9c41..2c0034ad234 100644
--- a/source/blender/blenkernel/BKE_brush.h
+++ b/source/blender/blenkernel/BKE_brush.h
@@ -69,7 +69,7 @@ BrushPainter *brush_painter_new(struct Brush *brush);
 void brush_painter_require_imbuf(BrushPainter *painter, short flt,
 	short texonly, int size);
 int brush_painter_paint(BrushPainter *painter, BrushFunc func, float *pos,
-	double time, void *user);
+	double time, float pressure, void *user);
 void brush_painter_break_stroke(BrushPainter *painter);
 void brush_painter_free(BrushPainter *painter);
 
diff --git a/source/blender/blenkernel/intern/brush.c b/source/blender/blenkernel/intern/brush.c
index 5ade66e4566..36e8c2137cc 100644
--- a/source/blender/blenkernel/intern/brush.c
+++ b/source/blender/blenkernel/intern/brush.c
@@ -299,6 +299,13 @@ void brush_check_exists(Brush **brush)
 
 /* Brush Sampling */
 
+/*static float taylor_approx_cos(float f)
+{
+	f = f*f;
+	f = 1.0f - f/2.0f + f*f/24.0f;
+	return f;
+}*/
+
 float brush_sample_falloff(Brush *brush, float dist)
 {
 	float a, outer, inner;
@@ -310,10 +317,12 @@ float brush_sample_falloff(Brush *brush, float dist)
 		return brush->alpha;
 	}
 	else if ((dist < outer) && (inner < outer)) {
-		/* formula used by sculpt:
-		   0.5f * (cos(3*(dist - inner)/(outer - inner)) + 1); */
 		a = sqrt((dist - inner)/(outer - inner));
 		return (1 - a)*brush->alpha;
+
+		/* formula used by sculpt, with taylor approx 
+		a = 0.5f*(taylor_approx_cos(3.0f*(dist - inner)/(outer - inner)) + 1.0f);
+		return a*brush->alpha; */
 	}
 	else 
 		return 0.0f;
@@ -470,6 +479,8 @@ struct BrushPainter {
 	double accumtime;		/* accumulated time since last paint op (airbrush) */
 	double lasttime;		/* time of last update */
 
+	float lastpressure;
+
 	short firsttouch;		/* first paint op */
 
 	float startsize;
@@ -720,24 +731,37 @@ void brush_painter_break_stroke(BrushPainter *painter)
 	painter->firsttouch= 1;
 }
 
-int brush_painter_paint(BrushPainter *painter, BrushFunc func, float *pos, double time, void *user)
+static void brush_apply_pressure(BrushPainter *painter, Brush *brush, float pressure)
+{
+	if (brush->flag & BRUSH_ALPHA_PRESSURE) 
+		brush->alpha = MAX2(0.0, painter->startalpha*pressure);
+	if (brush->flag & BRUSH_SIZE_PRESSURE)
+		brush->size = MAX2(1.0, painter->startsize*pressure);
+	if (brush->flag & BRUSH_RAD_PRESSURE)
+		brush->innerradius = MAX2(0.0, painter->startinnerradius*pressure);
+	if (brush->flag & BRUSH_SPACING_PRESSURE)
+		brush->spacing = MAX2(1.0, painter->startspacing*(1.5f-pressure));
+}
+
+int brush_painter_paint(BrushPainter *painter, BrushFunc func, float *pos, double time, float pressure, void *user)
 {
 	Brush *brush= painter->brush;
 	int totpaintops= 0;
 
+	if (pressure == 0.0f)
+		pressure = 1.0f;	/* zero pressure == not using tablet */
+
 	if (painter->firsttouch) {
 		/* paint exactly once on first touch */
 		painter->startpaintpos[0]= pos[0];
 		painter->startpaintpos[1]= pos[1];
 
+		brush_apply_pressure(painter, brush, pressure);
 		if (painter->cache.enabled)
 			brush_painter_refresh_cache(painter, pos);
 		totpaintops += func(user, painter->cache.ibuf, pos, pos);
 		
-		painter->lastpaintpos[0]= pos[0];
-		painter->lastpaintpos[1]= pos[1];
 		painter->lasttime= time;
-
 		painter->firsttouch= 0;
 	}
 #if 0
@@ -760,8 +784,10 @@ int brush_painter_paint(BrushPainter *painter, BrushFunc func, float *pos, doubl
 			paintpos[0]= painter->lastmousepos[0] + dmousepos[0]*step;
 			paintpos[1]= painter->lastmousepos[1] + dmousepos[1]*step;
 
-			if (painter->cache.enabled) brush_painter_refresh_cache(painter);
-			totpaintops += func(user, painter->cache.ibuf, painter->lastpaintpos, paintpos);
+			if (painter->cache.enabled)
+				brush_painter_refresh_cache(painter);
+			totpaintops += func(user, painter->cache.ibuf,
+				painter->lastpaintpos, paintpos);
 
 			painter->lastpaintpos[0]= paintpos[0];
 			painter->lastpaintpos[1]= paintpos[1];
@@ -774,15 +800,18 @@ int brush_painter_paint(BrushPainter *painter, BrushFunc func, float *pos, doubl
 #endif
 	else {
 		float startdistance, spacing, step, paintpos[2], dmousepos[2];
-		float brushsize = MAX2(1.0, brush->size);
+		float t, len, press;
 
-		/* compute brush spacing adapted to brush size */
-		spacing= brushsize*brush->spacing*0.01f;
+		/* compute brush spacing adapted to brush size, spacing may depend
+		   on pressure, so update it */
+		brush_apply_pressure(painter, brush, painter->lastpressure);
+		spacing= MAX2(1.0, brush->size)*brush->spacing*0.01f;
 
 		/* setup starting distance, direction vector and accumulated distance */
 		startdistance= painter->accumdistance;
 		Vec2Subf(dmousepos, pos, painter->lastmousepos);
-		painter->accumdistance += Normalise2(dmousepos);
+		len= Normalise2(dmousepos);
+		painter->accumdistance += len;
 
 		/* do paint op over unpainted distance */
 		while (painter->accumdistance >= spacing) {
@@ -790,8 +819,14 @@ int brush_painter_paint(BrushPainter *painter, BrushFunc func, float *pos, doubl
 			paintpos[0]= painter->lastmousepos[0] + dmousepos[0]*step;
 			paintpos[1]= painter->lastmousepos[1] + dmousepos[1]*step;
 
+			t = step/len;
+			press= (1.0-t)*painter->lastpressure + t*pressure;
+			brush_apply_pressure(painter, brush, press);
+			spacing= MAX2(1.0, brush->size)*brush->spacing*0.01f;
+
 			if (painter->cache.enabled)
 				brush_painter_refresh_cache(painter, paintpos);
+
 			totpaintops +=
 				func(user, painter->cache.ibuf, painter->lastpaintpos, paintpos);
 
@@ -815,6 +850,7 @@ int brush_painter_paint(BrushPainter *painter, BrushFunc func, float *pos, doubl
 				painter->accumtime -= painttime;
 
 			while (painter->accumtime >= brush->rate) {
+				brush_apply_pressure(painter, brush, pressure);
 				if (painter->cache.enabled)
 					brush_painter_refresh_cache(painter, paintpos);
 				totpaintops +=
@@ -828,6 +864,12 @@ int brush_painter_paint(BrushPainter *painter, BrushFunc func, float *pos, doubl
 
 	painter->lastmousepos[0]= pos[0];
 	painter->lastmousepos[1]= pos[1];
+	painter->lastpressure= pressure;
+
+	brush->alpha = painter->startalpha;
+	brush->size = painter->startsize;
+	brush->innerradius = painter->startinnerradius;
+	brush->spacing = painter->startspacing;
 
 	return totpaintops;
 }