In libmng-1.0.10/doc you can find two large PNG files:
Plan1.png and Plan2.png .
Both have alpha transparency and are interlaced.
fltk-2.0.x-r6970 - not handling interlace - offered a
horrible result.
The following patch allows to show a good result.
winfried
--- fl_png.cxx.orig 2010-02-21 15:07:19.000000000 +0100
+++ fl_png.cxx 2010-02-21 20:52:14.000000000 +0100
@@ -74,6 +74,8 @@
png_infop info_ptr;
png_uint_32 width, height;
int bit_depth, color_type;
+ int interlace_type = 0;
+ int pass, nr_passes = 0;
png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, 0,0,0);
@@ -117,16 +119,16 @@
png_read_info(png_ptr, info_ptr);
png_get_IHDR(png_ptr, info_ptr, &width, &height, &bit_depth,&color_type,
- NULL,NULL,NULL);
+ &interlace_type, NULL, NULL);
- if (color_type == PNG_COLOR_TYPE_PALETTE && bit_depth <= 8)
- png_set_expand(png_ptr);
+ if (color_type == PNG_COLOR_TYPE_PALETTE)
+ png_set_palette_to_rgb(png_ptr);
if (color_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8)
- png_set_expand(png_ptr);
+ png_set_expand_gray_1_2_4_to_8(png_ptr);
-/* if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS))
- png_set_expand(png_ptr);*/
+ if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS))
+ png_set_tRNS_to_alpha(png_ptr);
if (bit_depth == 16)
png_set_strip_16(png_ptr);
@@ -143,6 +145,8 @@
else
png_set_gamma(png_ptr, screen_gamma, 0.50);*/
+ nr_passes = png_set_interlace_handling(png_ptr);
+
png_read_update_info(png_ptr, info_ptr);
png_get_IHDR(png_ptr, info_ptr, &width, &height, &bit_depth,&color_type,
@@ -155,11 +159,30 @@
setpixeltype(alpha ? RGBM : RGB);
{ // avoid y initialization error in VC6 because of 'goto error' code
- for (unsigned y=0; y<height; y++) {
+ if(interlace_type)
+ {
+ for(pass = 0; pass < nr_passes; pass++)
+ {
+ for (unsigned y=0; y<height; y++)
+ {
+ uchar* b = linebuffer(y);
+ png_read_row(png_ptr, b, NULL);
+ }
+ }
+ for (unsigned y=0; y<height; y++)
+ {
+ uchar* b = linebuffer(y);
+ setpixels(b, y);
+ }
+ }
+ else // image not interlaced
+ for (unsigned y=0; y<height; y++)
+ {
uchar* b = linebuffer(y);
png_read_row(png_ptr, b, NULL);
setpixels(b, y);
- }
+ }
+
}
png_read_end(png_ptr, NULL);
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