shithub: libgraphics

Info  •  Files  •  Log  •  Branches

premultiply alpha when writing to color rasters

with this we can avoid duplicating the raster on
every framebufctl_(mem)draw() call.

we already apply gamma correction to the colors
before storage, so with this change the rasters
are effectively just Memimages.

--- a/color.c

+++ b/color.c

@@ -10,13 +10,13 @@

 ulong

 col2ul(Color c)

 {

-	uchar cbuf[4];

+	ulong l;

-	cbuf[0] = fclamp(c.a, 0, 1)*0xFF;

-	cbuf[1] = fclamp(c.b, 0, 1)*0xFF;

-	cbuf[2] = fclamp(c.g, 0, 1)*0xFF;

-	cbuf[3] = fclamp(c.r, 0, 1)*0xFF;

-	return cbuf[3]<<24 | cbuf[2]<<16 | cbuf[1]<<8 | cbuf[0];

+	l  = (int)(fclamp(c.a, 0, 1)*0xFF);

+	l |= (int)(fclamp(c.b, 0, 1)*0xFF) << 8;

+	l |= (int)(fclamp(c.g, 0, 1)*0xFF) << 16;

+	l |= (int)(fclamp(c.r, 0, 1)*0xFF) << 24;

+	return l;

 }

 Color

@@ -126,7 +126,7 @@

  * Equations 5.32 and 5.30 from “Display Encoding”, Real-Time Rendering 4th ed. § 5.6

  */

 //static double

-//_srgb2linear(double c)

+//srgb2linear1(double c)

 //{

 //	if(c > 0.04045)

 //		return pow((c + 0.055)/1.055, 2.4);

@@ -134,7 +134,7 @@

 //}

 //

 //static double

-//_linear2srgb(double c)

+//linear2srgb1(double c)

 //{

 //	if(c > 0.0031308)

 //		return 1.055*pow(c, 1.0/2.4) - 0.055;

@@ -142,7 +142,7 @@

 //}

 static double

-_srgb2linear(double c)

+srgb2linear1(double c)

 {

 	c = fclamp(c, 0, 1);

 	return srgb2lineartab[(int)(c*255)]/255.0;

@@ -149,7 +149,7 @@

 }

 static double

-_linear2srgb(double c)

+linear2srgb1(double c)

 {

 	c = fclamp(c, 0, 1);

 	return linear2srgbtab[(int)(c*255)]/255.0;

@@ -158,9 +158,9 @@

 Color

 srgb2linear(Color c)

 {

-	c.r = _srgb2linear(c.r);

-	c.g = _srgb2linear(c.g);

-	c.b = _srgb2linear(c.b);

+	c.r = srgb2linear1(c.r);

+	c.g = srgb2linear1(c.g);

+	c.b = srgb2linear1(c.b);

 	return c;

 }

@@ -167,9 +167,9 @@

 Color

 linear2srgb(Color c)

 {

-	c.r = _linear2srgb(c.r);

-	c.g = _linear2srgb(c.g);

-	c.b = _linear2srgb(c.b);

+	c.r = linear2srgb1(c.r);

+	c.g = linear2srgb1(c.g);

+	c.b = linear2srgb1(c.b);

 	return c;

 }

@@ -181,7 +181,7 @@

  * https://knarkowicz.wordpress.com/2016/01/06/aces-filmic-tone-mapping-curve/

  */

 static double

-_aces(double value)

+aces1(double value)

 {

 	double a = 2.51;

 	double b = 0.03;

@@ -195,9 +195,9 @@

 Color

 aces(Color c)

 {

-	c.r = _aces(c.r);

-	c.g = _aces(c.g);

-	c.b = _aces(c.b);

+	c.r = aces1(c.r);

+	c.g = aces1(c.g);

+	c.b = aces1(c.b);

 	return c;

 }

--- a/fb.c

+++ b/fb.c

@@ -129,23 +129,6 @@

 }

 static void

-premulalpha(Raster *r)

-{

-	Color c;

-	ulong *p, len;

-

-	len = Dx(r->r)*Dy(r->r);

-	p = r->data;

-	while(len--){

-		c = ul2col(*p);

-		c.r *= c.a;

-		c.g *= c.a;

-		c.b *= c.a;

-		*p++ = col2ul(c);

-	}

-}

-

-static void

 upscaledraw(Raster *fb, Image *dst, Point off, Point scale, uint filter)

 {

 	void (*filterfn)(ulong*, Raster*, Point, Point, ulong);

@@ -212,14 +195,6 @@

 		r = r2;

 	}

-	/* this means the raster is a color one, so duplicate it */

-	if(r2 == nil){

-		r2 = _allocraster(nil, r->r, COLOR32);

-		memmove(r2->data, r->data, Dx(r->r)*Dy(r->r)*4);

-		r = r2;

-	}

-	premulalpha(r);

-

 	if(scale.x > 1 || scale.y > 1){

 		upscaledraw(r, dst, off, scale, ctl->upfilter);

 		qunlock(ctl);

@@ -311,14 +286,6 @@

 		rasterconvF2C(r2, r);

 		r = r2;

 	}

-

-	/* this means the raster is a color one, so duplicate it */

-	if(r2 == nil){

-		r2 = _allocraster(nil, r->r, COLOR32);

-		memmove(r2->data, r->data, Dx(r->r)*Dy(r->r)*4);

-		r = r2;

-	}

-	premulalpha(r);

 	if(scale.x > 1 || scale.y > 1){

 		upscalememdraw(r, dst, off, scale, ctl->upfilter);

--- a/render.c

+++ b/render.c

@@ -31,6 +31,23 @@

 	_addvattr(sp->v, id, type, val);

 }

+#define mulalpha1(a, v, tmp)	(tmp=(a)*(v)+128, (tmp+(tmp>>8))>>8)

+

+static ulong

+mulalpha(ulong c)

+{

+	ushort r, g, b, a, t;

+

+	a = c     & 0xff;

+	b = c>>8  & 0xff;

+	g = c>>16 & 0xff;

+	r = c>>24 & 0xff;

+	r = mulalpha1(a, r, t);

+	g = mulalpha1(a, g, t);

+	b = mulalpha1(a, b, t);

+	return (r<<24)|(g<<16)|(b<<8)|a;

+}

+

 static void

 sparams_toraster(Shaderparams *sp, char *rname, void *v)

 {

@@ -49,7 +66,7 @@

 	switch(r->chan){

 	case COLOR32:

-		c = col2ul(*(Color*)v);

+		c = mulalpha(col2ul(*(Color*)v));

 		_rasterput(r, sp->p, &c);

 		break;

 	case FLOAT32:

@@ -70,7 +87,7 @@

 //		c = subpt3(Vec3(1,1,1), subpt3(dc, c));

 //		c = subpt3(addpt3(dc, c), Vec3(1,1,1));

 	}

-	putpixel(fb, p, col2ul(linear2srgb(c)));

+	putpixel(fb, p, mulalpha(col2ul(linear2srgb(c))));

 }

 static int

-- 

⑨