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add reading scaled png images

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kub 2024-03-20 23:40:37 +01:00
parent 82b4854771
commit 4563c13167
2 changed files with 38 additions and 0 deletions
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37
readpng.c
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@ -67,6 +67,43 @@ int readpng(void *dest, const char *fname, readpng_what what, int req_w, int req
switch (what)
{
case READPNG_SCALE:
{
int height, width, x_ofs = 0, y_ofs = 0;
unsigned short *dst = dest;
int x_scale, y_scale, x_pos, y_pos; // Q16
if (png_get_bit_depth(png_ptr, info_ptr) != 8)
{
lprintf(__FILE__ ": scaled image uses %ibpc, needed 8bpc\n", png_get_bit_depth(png_ptr, info_ptr));
break;
}
width = png_get_image_width(png_ptr, info_ptr);
x_scale = width*65536 / req_w;
height = png_get_image_height(png_ptr, info_ptr);
y_scale = height*65536 / req_h;
if (x_scale < y_scale)
x_scale = y_scale;
else y_scale = x_scale;
x_ofs = req_w - width*65536 / x_scale;
y_ofs = req_h - height*65536 / y_scale;
dst += y_ofs/2*req_w + x_ofs/2;
for (y_pos = 0; y_pos < height*65536; y_pos += y_scale+1)
{
unsigned char *src = row_ptr[y_pos >> 16];
int len = 0;
for (x_pos = 0; x_pos < width*65536; x_pos += x_scale+1, len++)
{
int o = 3*(x_pos >> 16);
// TODO: could use bilinear if upsampling?
*dst++ = PXMAKE(src[o], src[o+1], src[o+2]);
}
dst += req_w - len;
}
break;
}
case READPNG_BG:
{
int height, width, h, x_ofs = 0, y_ofs = 0;

1
readpng.h
View file

@ -7,6 +7,7 @@ typedef enum
READPNG_FONT,
READPNG_SELECTOR,
READPNG_24,
READPNG_SCALE,
}
readpng_what;