libpixelflinger/buffer.cpp - android_system_core - Gitiles

 /* libs/pixelflinger/buffer.cpp
 **
 ** Copyright 2006, The Android Open Source Project
 **
 ** Licensed under the Apache License, Version 2.0 (the "License");
 ** you may not use this file except in compliance with the License.
 ** You may obtain a copy of the License at
 **
 **     http://www.apache.org/licenses/LICENSE-2.0
 **
 ** Unless required by applicable law or agreed to in writing, software
 ** distributed under the License is distributed on an "AS IS" BASIS,
 ** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 ** See the License for the specific language governing permissions and
 ** limitations under the License.
 */


 #include <assert.h>

 #include <android-base/macros.h>

 #include "buffer.h"

 namespace android {
 // ----------------------------------------------------------------------------

 static void read_pixel(const surface_t* s, context_t* c,
         uint32_t x, uint32_t y, pixel_t* pixel);
 static void write_pixel(const surface_t* s, context_t* c,
         uint32_t x, uint32_t y, const pixel_t* pixel);
 static void readRGB565(const surface_t* s, context_t* c,
         uint32_t x, uint32_t y, pixel_t* pixel);
 static void readABGR8888(const surface_t* s, context_t* c,
         uint32_t x, uint32_t y, pixel_t* pixel);

 static uint32_t logic_op(int op, uint32_t s, uint32_t d);
 static uint32_t extract(uint32_t v, int h, int l, int bits);
 static uint32_t expand(uint32_t v, int sbits, int dbits);
 static uint32_t downshift_component(uint32_t in, uint32_t v,
         int sh, int sl, int dh, int dl, int ch, int cl, int dither);

 // ----------------------------------------------------------------------------

 void ggl_init_texture(context_t* c)
 {
     for (int i=0 ; i<GGL_TEXTURE_UNIT_COUNT ; i++) {
         texture_t& t = c->state.texture[i];
         t.s_coord = GGL_ONE_TO_ONE;
         t.t_coord = GGL_ONE_TO_ONE;
         t.s_wrap = GGL_REPEAT;
         t.t_wrap = GGL_REPEAT;
         t.min_filter = GGL_NEAREST;
         t.mag_filter = GGL_NEAREST;
         t.env = GGL_MODULATE;
     }
     c->activeTMU = &(c->state.texture[0]);
 }

 void ggl_set_surface(context_t* c, surface_t* dst, const GGLSurface* src)
 {
     dst->width = src->width;
     dst->height = src->height;
     dst->stride = src->stride;
     dst->data = src->data;
     dst->format = src->format;
     dst->dirty = 1;
     if (__builtin_expect(dst->stride < 0, false)) {
         const GGLFormat& pixelFormat(c->formats[dst->format]);
         const int32_t bpr = -dst->stride * pixelFormat.size;
         dst->data += bpr * (dst->height-1);
     }
 }

 static void pick_read_write(surface_t* s)
 {
     // Choose best reader/writers.
     switch (s->format) {
         case GGL_PIXEL_FORMAT_RGBA_8888:    s->read = readABGR8888;  break;
         case GGL_PIXEL_FORMAT_RGB_565:      s->read = readRGB565;    break;
         default:                            s->read = read_pixel;    break;
     }
     s->write = write_pixel;
 }

 void ggl_pick_texture(context_t* c)
 {
     for (int i=0 ; i<GGL_TEXTURE_UNIT_COUNT ; ++i) {
         surface_t& s = c->state.texture[i].surface;
         if ((!c->state.texture[i].enable) || (!s.dirty))
             continue;
         s.dirty = 0;
         pick_read_write(&s);
         generated_tex_vars_t& gen = c->generated_vars.texture[i];
         gen.width   = s.width;
         gen.height  = s.height;
         gen.stride  = s.stride;
         gen.data    = uintptr_t(s.data);
     }
 }

 void ggl_pick_cb(context_t* c)
 {
     surface_t& s = c->state.buffers.color;
     if (s.dirty) {
         s.dirty = 0;
         pick_read_write(&s);
     }
 }

 // ----------------------------------------------------------------------------

 void read_pixel(const surface_t* s, context_t* c,
         uint32_t x, uint32_t y, pixel_t* pixel)
 {
     assert((x < s->width) && (y < s->height));

     const GGLFormat* f = &(c->formats[s->format]);
     int32_t index = x + (s->stride * y);
     uint8_t* const data = s->data + index * f->size;
     uint32_t v = 0;
     switch (f->size) {
         case 1:		v = *data;									break;
         case 2:		v = *(uint16_t*)data;						break;
         case 3:		v = (data[2]<<16)|(data[1]<<8)|data[0];     break;
         case 4:		v = GGL_RGBA_TO_HOST(*(uint32_t*)data);		break;
     }
     for (int i=0 ; i<4 ; i++) {
         pixel->s[i] = f->c[i].h - f->c[i].l;
         if (pixel->s[i])
             pixel->c[i] = extract(v,  f->c[i].h,  f->c[i].l, f->size*8);
     }
 }

 void readRGB565(const surface_t* s, context_t* /*c*/,
         uint32_t x, uint32_t y, pixel_t* pixel)
 {
     uint16_t v = *(reinterpret_cast<uint16_t*>(s->data) + (x + (s->stride * y)));
     pixel->c[0] = 0;
     pixel->c[1] = v>>11;
     pixel->c[2] = (v>>5)&0x3F;
     pixel->c[3] = v&0x1F;
     pixel->s[0] = 0;
     pixel->s[1] = 5;
     pixel->s[2] = 6;
     pixel->s[3] = 5;
 }

 void readABGR8888(const surface_t* s, context_t* /*c*/,
         uint32_t x, uint32_t y, pixel_t* pixel)
 {
     uint32_t v = *(reinterpret_cast<uint32_t*>(s->data) + (x + (s->stride * y)));
     v = GGL_RGBA_TO_HOST(v);
     pixel->c[0] = v>>24;        // A
     pixel->c[1] = v&0xFF;       // R
     pixel->c[2] = (v>>8)&0xFF;  // G
     pixel->c[3] = (v>>16)&0xFF; // B
     pixel->s[0] =
     pixel->s[1] =
     pixel->s[2] =
     pixel->s[3] = 8;
 }

 void write_pixel(const surface_t* s, context_t* c,
         uint32_t x, uint32_t y, const pixel_t* pixel)
 {
     assert((x < s->width) && (y < s->height));

     int dither = -1;
     if (c->state.enables & GGL_ENABLE_DITHER) {
         dither = c->ditherMatrix[ (x & GGL_DITHER_MASK) +
                 ((y & GGL_DITHER_MASK)<<GGL_DITHER_ORDER_SHIFT) ];
     }

     const GGLFormat* f = &(c->formats[s->format]);
     int32_t index = x + (s->stride * y);
     uint8_t* const data = s->data + index * f->size;

     uint32_t mask = 0;
     uint32_t v = 0;
     for (int i=0 ; i<4 ; i++) {
         const int component_mask = 1 << i;
         if (f->components>=GGL_LUMINANCE &&
                 (i==GGLFormat::GREEN || i==GGLFormat::BLUE)) {
             // destinations L formats don't have G or B
             continue;
         }
         const int l = f->c[i].l;
         const int h = f->c[i].h;
         if (h && (c->state.mask.color & component_mask)) {
             mask |= (((1<<(h-l))-1)<<l);
             uint32_t u = pixel->c[i];
             int32_t pixelSize = pixel->s[i];
             if (pixelSize < (h-l)) {
                 u = expand(u, pixelSize, h-l);
                 pixelSize = h-l;
             }
             v = downshift_component(v, u, pixelSize, 0, h, l, 0, 0, dither);
         }
     }

     if ((c->state.mask.color != 0xF) ||
         (c->state.enables & GGL_ENABLE_LOGIC_OP)) {
         uint32_t d = 0;
         switch (f->size) {
             case 1:	d = *data;									break;
             case 2:	d = *(uint16_t*)data;						break;
             case 3:	d = (data[2]<<16)|(data[1]<<8)|data[0];     break;
             case 4:	d = GGL_RGBA_TO_HOST(*(uint32_t*)data);		break;
         }
         if (c->state.enables & GGL_ENABLE_LOGIC_OP) {
             v = logic_op(c->state.logic_op.opcode, v, d);
             v &= mask;
         }
         v |= (d & ~mask);
     }

     switch (f->size) {
         case 1:		*data = v;									break;
         case 2:		*(uint16_t*)data = v;						break;
         case 3:
             data[0] = v;
             data[1] = v>>8;
             data[2] = v>>16;
             break;
         case 4:		*(uint32_t*)data = GGL_HOST_TO_RGBA(v);     break;
     }
 }

 static uint32_t logic_op(int op, uint32_t s, uint32_t d)
 {
     switch(op) {
     case GGL_CLEAR:         return 0;
     case GGL_AND:           return s & d;
     case GGL_AND_REVERSE:   return s & ~d;
     case GGL_COPY:          return s;
     case GGL_AND_INVERTED:  return ~s & d;
     case GGL_NOOP:          return d;
     case GGL_XOR:           return s ^ d;
     case GGL_OR:            return s | d;
     case GGL_NOR:           return ~(s | d);
     case GGL_EQUIV:         return ~(s ^ d);
     case GGL_INVERT:        return ~d;
     case GGL_OR_REVERSE:    return s | ~d;
     case GGL_COPY_INVERTED: return ~s;
     case GGL_OR_INVERTED:   return ~s | d;
     case GGL_NAND:          return ~(s & d);
     case GGL_SET:           return ~0;
     };
     return s;
 }


 uint32_t ggl_expand(uint32_t v, int sbits, int dbits)
 {
     return expand(v, sbits, dbits);
 }

 uint32_t ggl_pack_color(context_t* c, int32_t format,
         GGLcolor r, GGLcolor g, GGLcolor b, GGLcolor a)
 {
     const GGLFormat* f = &(c->formats[format]);
     uint32_t p = 0;
     const int32_t hbits = GGL_COLOR_BITS;
     const int32_t lbits = GGL_COLOR_BITS - 8;
     p = downshift_component(p, r,   hbits, lbits,  f->rh, f->rl, 0, 1, -1);
     p = downshift_component(p, g,   hbits, lbits,  f->gh, f->gl, 0, 1, -1);
     p = downshift_component(p, b,   hbits, lbits,  f->bh, f->bl, 0, 1, -1);
     p = downshift_component(p, a,   hbits, lbits,  f->ah, f->al, 0, 1, -1);
     switch (f->size) {
         case 1:
             p |= p << 8;
             FALLTHROUGH_INTENDED;
         case 2:
             p |= p << 16;
     }
     return p;
 }

 // ----------------------------------------------------------------------------

 // extract a component from a word
 uint32_t extract(uint32_t v, int h, int l, int bits)
 {
 	assert(h);
 	if (l) {
 		v >>= l;
 	}
 	if (h != bits) {
 		v &= (1<<(h-l))-1;
 	}
 	return v;
 }

 // expand a component from sbits to dbits
 uint32_t expand(uint32_t v, int sbits, int dbits)
 {
     if (dbits > sbits) {
         assert(sbits);
         if (sbits==1) {
             v = (v<<dbits) - v;
         } else {
             if (dbits % sbits) {
                 v <<= (dbits-sbits);
                 dbits -= sbits;
                 do {
                     v |= v>>sbits;
                     dbits -= sbits;
                     sbits *= 2;
                 } while (dbits>0);
             } else {
                 dbits -= sbits;
                 do {
                     v |= v<<sbits;
                     dbits -= sbits;
                     if (sbits*2 < dbits) {
                         sbits *= 2;
                     }
                 } while (dbits > 0);
             }
         }
     }
 	return v;
 }

 // downsample a component from sbits to dbits
 // and shift / construct the pixel
 uint32_t downshift_component(	uint32_t in, uint32_t v,
                                 int sh, int sl,		// src
                                 int dh, int dl,		// dst
                                 int ch, int cl,		// clear
                                 int dither)
 {
 	const int sbits = sh-sl;
 	const int dbits = dh-dl;

 	assert(sbits>=dbits);


     if (sbits>dbits) {
         if (dither>=0) {
             v -= (v>>dbits);				// fix up
             const int shift = (GGL_DITHER_BITS - (sbits-dbits));
             if (shift >= 0)   v += (dither >> shift) << sl;
             else              v += (dither << (-shift)) << sl;
         } else {
             // don't do that right now, so we can reproduce the same
             // artifacts we get on ARM (Where we don't do this)
             // -> this is not really needed if we don't dither
             //if (dBits > 1) { // result already OK if dBits==1
             //    v -= (v>>dbits);				// fix up
             //    v += 1 << ((sbits-dbits)-1);	// rounding
             //}
         }
     }


 	// we need to clear the high bits of the source
 	if (ch) {
 		v <<= 32-sh;
 		sl += 32-sh;
         sh = 32;
 	}

 	if (dl) {
 		if (cl || (sbits>dbits)) {
 			v >>= sh-dbits;
 			sl = 0;
 			sh = dbits;
             in |= v<<dl;
 		} else {
 			// sbits==dbits and we don't need to clean the lower bits
 			// so we just have to shift the component to the right location
             int shift = dh-sh;
             in |= v<<shift;
 		}
 	} else {
 		// destination starts at bit 0
 		// ie: sh-dh == sh-dbits
 		int shift = sh-dh;
 		if (shift > 0)      in |= v>>shift;
 		else if (shift < 0) in |= v<<shift;
 		else                in |= v;
 	}
 	return in;
 }

 // ----------------------------------------------------------------------------
 }; // namespace android
	/* libs/pixelflinger/buffer.cpp
	**
	** Copyright 2006, The Android Open Source Project
	**
	** Licensed under the Apache License, Version 2.0 (the "License");
	** you may not use this file except in compliance with the License.
	** You may obtain a copy of the License at
	**
	** http://www.apache.org/licenses/LICENSE-2.0
	**
	** Unless required by applicable law or agreed to in writing, software
	** distributed under the License is distributed on an "AS IS" BASIS,
	** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	** See the License for the specific language governing permissions and
	** limitations under the License.
	*/


	#include <assert.h>

	#include <android-base/macros.h>

	#include "buffer.h"

	namespace android {
	// ----------------------------------------------------------------------------

	static void read_pixel(const surface_t* s, context_t* c,
	uint32_t x, uint32_t y, pixel_t* pixel);
	static void write_pixel(const surface_t* s, context_t* c,
	uint32_t x, uint32_t y, const pixel_t* pixel);
	static void readRGB565(const surface_t* s, context_t* c,
	uint32_t x, uint32_t y, pixel_t* pixel);
	static void readABGR8888(const surface_t* s, context_t* c,
	uint32_t x, uint32_t y, pixel_t* pixel);

	static uint32_t logic_op(int op, uint32_t s, uint32_t d);
	static uint32_t extract(uint32_t v, int h, int l, int bits);
	static uint32_t expand(uint32_t v, int sbits, int dbits);
	static uint32_t downshift_component(uint32_t in, uint32_t v,
	int sh, int sl, int dh, int dl, int ch, int cl, int dither);

	// ----------------------------------------------------------------------------

	void ggl_init_texture(context_t* c)
	{
	for (int i=0 ; i<GGL_TEXTURE_UNIT_COUNT ; i++) {
	texture_t& t = c->state.texture[i];
	t.s_coord = GGL_ONE_TO_ONE;
	t.t_coord = GGL_ONE_TO_ONE;
	t.s_wrap = GGL_REPEAT;
	t.t_wrap = GGL_REPEAT;
	t.min_filter = GGL_NEAREST;
	t.mag_filter = GGL_NEAREST;
	t.env = GGL_MODULATE;
	}
	c->activeTMU = &(c->state.texture[0]);
	}

	void ggl_set_surface(context_t* c, surface_t* dst, const GGLSurface* src)
	{
	dst->width = src->width;
	dst->height = src->height;
	dst->stride = src->stride;
	dst->data = src->data;
	dst->format = src->format;
	dst->dirty = 1;
	if (__builtin_expect(dst->stride < 0, false)) {
	const GGLFormat& pixelFormat(c->formats[dst->format]);
	const int32_t bpr = -dst->stride * pixelFormat.size;
	dst->data += bpr * (dst->height-1);
	}
	}

	static void pick_read_write(surface_t* s)
	{
	// Choose best reader/writers.
	switch (s->format) {
	case GGL_PIXEL_FORMAT_RGBA_8888: s->read = readABGR8888; break;
	case GGL_PIXEL_FORMAT_RGB_565: s->read = readRGB565; break;
	default: s->read = read_pixel; break;
	}
	s->write = write_pixel;
	}

	void ggl_pick_texture(context_t* c)
	{
	for (int i=0 ; i<GGL_TEXTURE_UNIT_COUNT ; ++i) {
	surface_t& s = c->state.texture[i].surface;
	if ((!c->state.texture[i].enable) \|\| (!s.dirty))
	continue;
	s.dirty = 0;
	pick_read_write(&s);
	generated_tex_vars_t& gen = c->generated_vars.texture[i];
	gen.width = s.width;
	gen.height = s.height;
	gen.stride = s.stride;
	gen.data = uintptr_t(s.data);
	}
	}

	void ggl_pick_cb(context_t* c)
	{
	surface_t& s = c->state.buffers.color;
	if (s.dirty) {
	s.dirty = 0;
	pick_read_write(&s);
	}
	}

	// ----------------------------------------------------------------------------

	void read_pixel(const surface_t* s, context_t* c,
	uint32_t x, uint32_t y, pixel_t* pixel)
	{
	assert((x < s->width) && (y < s->height));

	const GGLFormat* f = &(c->formats[s->format]);
	int32_t index = x + (s->stride * y);
	uint8_t* const data = s->data + index * f->size;
	uint32_t v = 0;
	switch (f->size) {
	case 1: v = *data; break;
	case 2: v = (uint16_t)data; break;
	case 3: v = (data[2]<<16)\|(data[1]<<8)\|data[0]; break;
	case 4: v = GGL_RGBA_TO_HOST((uint32_t)data); break;
	}
	for (int i=0 ; i<4 ; i++) {
	pixel->s[i] = f->c[i].h - f->c[i].l;
	if (pixel->s[i])
	pixel->c[i] = extract(v, f->c[i].h, f->c[i].l, f->size*8);
	}
	}

	void readRGB565(const surface_t* s, context_t* /c/,
	uint32_t x, uint32_t y, pixel_t* pixel)
	{
	uint16_t v = (reinterpret_cast<uint16_t>(s->data) + (x + (s->stride * y)));
	pixel->c[0] = 0;
	pixel->c[1] = v>>11;
	pixel->c[2] = (v>>5)&0x3F;
	pixel->c[3] = v&0x1F;
	pixel->s[0] = 0;
	pixel->s[1] = 5;
	pixel->s[2] = 6;
	pixel->s[3] = 5;
	}

	void readABGR8888(const surface_t* s, context_t* /c/,
	uint32_t x, uint32_t y, pixel_t* pixel)
	{
	uint32_t v = (reinterpret_cast<uint32_t>(s->data) + (x + (s->stride * y)));
	v = GGL_RGBA_TO_HOST(v);
	pixel->c[0] = v>>24; // A
	pixel->c[1] = v&0xFF; // R
	pixel->c[2] = (v>>8)&0xFF; // G
	pixel->c[3] = (v>>16)&0xFF; // B
	pixel->s[0] =
	pixel->s[1] =
	pixel->s[2] =
	pixel->s[3] = 8;
	}

	void write_pixel(const surface_t* s, context_t* c,
	uint32_t x, uint32_t y, const pixel_t* pixel)
	{
	assert((x < s->width) && (y < s->height));

	int dither = -1;
	if (c->state.enables & GGL_ENABLE_DITHER) {
	dither = c->ditherMatrix[ (x & GGL_DITHER_MASK) +
	((y & GGL_DITHER_MASK)<<GGL_DITHER_ORDER_SHIFT) ];
	}

	const GGLFormat* f = &(c->formats[s->format]);
	int32_t index = x + (s->stride * y);
	uint8_t* const data = s->data + index * f->size;

	uint32_t mask = 0;
	uint32_t v = 0;
	for (int i=0 ; i<4 ; i++) {
	const int component_mask = 1 << i;
	if (f->components>=GGL_LUMINANCE &&
	(i==GGLFormat::GREEN \|\| i==GGLFormat::BLUE)) {
	// destinations L formats don't have G or B
	continue;
	}
	const int l = f->c[i].l;
	const int h = f->c[i].h;
	if (h && (c->state.mask.color & component_mask)) {
	mask \|= (((1<<(h-l))-1)<<l);
	uint32_t u = pixel->c[i];
	int32_t pixelSize = pixel->s[i];
	if (pixelSize < (h-l)) {
	u = expand(u, pixelSize, h-l);
	pixelSize = h-l;
	}
	v = downshift_component(v, u, pixelSize, 0, h, l, 0, 0, dither);
	}
	}

	if ((c->state.mask.color != 0xF) \|\|
	(c->state.enables & GGL_ENABLE_LOGIC_OP)) {
	uint32_t d = 0;
	switch (f->size) {
	case 1: d = *data; break;
	case 2: d = (uint16_t)data; break;
	case 3: d = (data[2]<<16)\|(data[1]<<8)\|data[0]; break;
	case 4: d = GGL_RGBA_TO_HOST((uint32_t)data); break;
	}
	if (c->state.enables & GGL_ENABLE_LOGIC_OP) {
	v = logic_op(c->state.logic_op.opcode, v, d);
	v &= mask;
	}
	v \|= (d & ~mask);
	}

	switch (f->size) {
	case 1: *data = v; break;
	case 2: (uint16_t)data = v; break;
	case 3:
	data[0] = v;
	data[1] = v>>8;
	data[2] = v>>16;
	break;
	case 4: (uint32_t)data = GGL_HOST_TO_RGBA(v); break;
	}
	}

	static uint32_t logic_op(int op, uint32_t s, uint32_t d)
	{
	switch(op) {
	case GGL_CLEAR: return 0;
	case GGL_AND: return s & d;
	case GGL_AND_REVERSE: return s & ~d;
	case GGL_COPY: return s;
	case GGL_AND_INVERTED: return ~s & d;
	case GGL_NOOP: return d;
	case GGL_XOR: return s ^ d;
	case GGL_OR: return s \| d;
	case GGL_NOR: return ~(s \| d);
	case GGL_EQUIV: return ~(s ^ d);
	case GGL_INVERT: return ~d;
	case GGL_OR_REVERSE: return s \| ~d;
	case GGL_COPY_INVERTED: return ~s;
	case GGL_OR_INVERTED: return ~s \| d;
	case GGL_NAND: return ~(s & d);
	case GGL_SET: return ~0;
	};
	return s;
	}


	uint32_t ggl_expand(uint32_t v, int sbits, int dbits)
	{
	return expand(v, sbits, dbits);
	}

	uint32_t ggl_pack_color(context_t* c, int32_t format,
	GGLcolor r, GGLcolor g, GGLcolor b, GGLcolor a)
	{
	const GGLFormat* f = &(c->formats[format]);
	uint32_t p = 0;
	const int32_t hbits = GGL_COLOR_BITS;
	const int32_t lbits = GGL_COLOR_BITS - 8;
	p = downshift_component(p, r, hbits, lbits, f->rh, f->rl, 0, 1, -1);
	p = downshift_component(p, g, hbits, lbits, f->gh, f->gl, 0, 1, -1);
	p = downshift_component(p, b, hbits, lbits, f->bh, f->bl, 0, 1, -1);
	p = downshift_component(p, a, hbits, lbits, f->ah, f->al, 0, 1, -1);
	switch (f->size) {
	case 1:
	p \|= p << 8;
	FALLTHROUGH_INTENDED;
	case 2:
	p \|= p << 16;
	}
	return p;
	}

	// ----------------------------------------------------------------------------

	// extract a component from a word
	uint32_t extract(uint32_t v, int h, int l, int bits)
	{
	assert(h);
	if (l) {
	v >>= l;
	}
	if (h != bits) {
	v &= (1<<(h-l))-1;
	}
	return v;
	}

	// expand a component from sbits to dbits
	uint32_t expand(uint32_t v, int sbits, int dbits)
	{
	if (dbits > sbits) {
	assert(sbits);
	if (sbits==1) {
	v = (v<<dbits) - v;
	} else {
	if (dbits % sbits) {
	v <<= (dbits-sbits);
	dbits -= sbits;
	do {
	v \|= v>>sbits;
	dbits -= sbits;
	sbits *= 2;
	} while (dbits>0);
	} else {
	dbits -= sbits;
	do {
	v \|= v<<sbits;
	dbits -= sbits;
	if (sbits*2 < dbits) {
	sbits *= 2;
	}
	} while (dbits > 0);
	}
	}
	}
	return v;
	}

	// downsample a component from sbits to dbits
	// and shift / construct the pixel
	uint32_t downshift_component( uint32_t in, uint32_t v,
	int sh, int sl, // src
	int dh, int dl, // dst
	int ch, int cl, // clear
	int dither)
	{
	const int sbits = sh-sl;
	const int dbits = dh-dl;

	assert(sbits>=dbits);


	if (sbits>dbits) {
	if (dither>=0) {
	v -= (v>>dbits); // fix up
	const int shift = (GGL_DITHER_BITS - (sbits-dbits));
	if (shift >= 0) v += (dither >> shift) << sl;
	else v += (dither << (-shift)) << sl;
	} else {
	// don't do that right now, so we can reproduce the same
	// artifacts we get on ARM (Where we don't do this)
	// -> this is not really needed if we don't dither
	//if (dBits > 1) { // result already OK if dBits==1
	// v -= (v>>dbits); // fix up
	// v += 1 << ((sbits-dbits)-1); // rounding
	//}
	}
	}


	// we need to clear the high bits of the source
	if (ch) {
	v <<= 32-sh;
	sl += 32-sh;
	sh = 32;
	}

	if (dl) {
	if (cl \|\| (sbits>dbits)) {
	v >>= sh-dbits;
	sl = 0;
	sh = dbits;
	in \|= v<<dl;
	} else {
	// sbits==dbits and we don't need to clean the lower bits
	// so we just have to shift the component to the right location
	int shift = dh-sh;
	in \|= v<<shift;
	}
	} else {
	// destination starts at bit 0
	// ie: sh-dh == sh-dbits
	int shift = sh-dh;
	if (shift > 0) in \|= v>>shift;
	else if (shift < 0) in \|= v<<shift;
	else in \|= v;
	}
	return in;
	}

	// ----------------------------------------------------------------------------
	}; // namespace android