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Dither colors in non-default low depth color path

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This patch modifies the low color mode (slow) path
to dither the colors before flushing them to the
scanout buffer.  This improves the output quality
in those corner cases.
This commit is contained in:
Charlie Brej 2008-10-27 12:49:06 -04:00 • committed by Ray Strode
parent 23530e8f84
commit d3584b4e85
1 changed files with 31 additions and 10 deletions
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41
src/libply/ply-frame-buffer.c
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@ -68,6 +68,10 @@ struct _ply_frame_buffer
uint32_t bits_for_blue;
uint32_t bits_for_alpha;
int32_t dither_red;
int32_t dither_green;
int32_t dither_blue;
unsigned int bytes_per_pixel;
unsigned int row_stride;
@ -315,6 +319,10 @@ ply_frame_buffer_query_device (ply_frame_buffer_t *buffer)
buffer->bytes_per_pixel = variable_screen_info.bits_per_pixel >> 3;
buffer->row_stride = fixed_screen_info.line_length / buffer->bytes_per_pixel;
buffer->size = buffer->area.height * buffer->row_stride * buffer->bytes_per_pixel;
buffer->dither_red = 0;
buffer->dither_green = 0;
buffer->dither_blue = 0;
if (buffer->bytes_per_pixel == 4 &&
buffer->red_bit_position == 16 && buffer->bits_for_red == 8 &&
@ -340,24 +348,37 @@ ply_frame_buffer_map_to_device (ply_frame_buffer_t *buffer)
return buffer->map_address != MAP_FAILED;
}
__attribute__((__pure__))
static inline uint_fast32_t
ply_frame_buffer_pixel_value_to_device_pixel_value (ply_frame_buffer_t *buffer,
uint32_t pixel_value)
{
uint8_t r, g, b, a;
int orig_r, orig_g, orig_b, orig_a;
int i;
orig_a = pixel_value >> 24;
a = orig_a >> (8 - buffer->bits_for_alpha);
a = pixel_value >> 24;
a >>= (8 - buffer->bits_for_alpha);
orig_r = ((pixel_value >> 16) & 0xff) - buffer->dither_red;
r = CLAMP(orig_r, 0, 255) >> (8 - buffer->bits_for_red);
r = (pixel_value >> 16) & 0xff;
r >>= (8 - buffer->bits_for_red);
orig_g = ((pixel_value >> 8) & 0xff) - buffer->dither_green;
g = CLAMP(orig_g, 0, 255) >> (8 - buffer->bits_for_green);
g = (pixel_value >> 8) & 0xff;
g >>= (8 - buffer->bits_for_green);
b = pixel_value & 0xff;
b >>= (8 - buffer->bits_for_blue);
orig_b = (pixel_value & 0xff) - buffer->dither_blue;
b = CLAMP(orig_b, 0, 255) >> (8 - buffer->bits_for_blue);
uint8_t new_r = r << (8 - buffer->bits_for_red);
uint8_t new_g = g << (8 - buffer->bits_for_green);
uint8_t new_b = b << (8 - buffer->bits_for_blue);
for (i=buffer->bits_for_red; i<8; i*=2) new_r |= new_r >> i;
for (i=buffer->bits_for_green; i<8; i*=2) new_g |= new_g >> i;
for (i=buffer->bits_for_blue; i<8; i*=2) new_b |= new_b >> i;
buffer->dither_red = new_r - orig_r;
buffer->dither_green = new_g - orig_g;
buffer->dither_blue = new_b - orig_b;
return ((a << buffer->alpha_bit_position)
| (r << buffer->red_bit_position)