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gif: Frame decoding: Simplify transparency check.

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This commit is contained in:
Michael Drake 2021-04-04 11:54:22 +01:00 committed by Michael Drake
parent 663bf07aac
commit 7426c3d500
1 changed files with 10 additions and 4 deletions
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14
libvips/foreign/libnsgif/libnsgif.c
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@ -42,6 +42,9 @@
/** Transparent colour */
#define GIF_TRANSPARENT_COLOUR 0x00
/** No transparency */
#define GIF_NO_TRANSPARENCY (0xFFFFFFFFu)
/* GIF Flags */
#define GIF_FRAME_COMBINE 1
#define GIF_FRAME_CLEAR 2
@ -630,6 +633,7 @@ gif__decode(gif_animation *gif,
unsigned int *restrict frame_data,
unsigned int *restrict colour_table)
{
unsigned int transparency_index;
const uint8_t *stack_base;
const uint8_t *stack_pos;
uint32_t written = 0;
@ -644,6 +648,10 @@ gif__decode(gif_animation *gif,
return gif_error_from_lzw(res);
}
transparency_index = gif->frames[frame].transparency ?
gif->frames[frame].transparency_index :
GIF_NO_TRANSPARENCY;
stack_pos = stack_base;
for (unsigned int y = 0; y < height; y++) {
unsigned int x;
@ -667,11 +675,9 @@ gif__decode(gif_animation *gif,
x -= burst_bytes;
written -= burst_bytes;
while (burst_bytes-- > 0) {
register unsigned char colour;
register unsigned int colour;
colour = *stack_pos++;
if (((gif->frames[frame].transparency) &&
(colour != gif->frames[frame].transparency_index)) ||
(!gif->frames[frame].transparency)) {
if (colour != transparency_index) {
*frame_scanline = colour_table[colour];
}
frame_scanline++;