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plug-ins: bmp import - add/clarify some comments

This commit is contained in:
Rupert 2024-12-21 13:44:06 +01:00 committed by Jacob Boerema
parent 5db4955d4d
commit d48ce04291
1 changed files with 11 additions and 6 deletions
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17
plug-ins/file-bmp/bmp-load.c
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@ -199,7 +199,7 @@ read_colormap (FILE *fd,
return FALSE;
}
/* Bitmap save the colors in another order! But change only once! */
/* BMP colormap entries are in BGR order */
buffer[3 * i + 0] = rgb[2];
buffer[3 * i + 1] = rgb[1];
@ -348,8 +348,6 @@ load_image (GFile *gfile, GError **error)
goto out;
}
/* What kind of bitmap is it? */
/* OS/2 headers store width and height as unsigned, Windows headers as signed.
* We make no attempt to distinguish between those (which would be possible
* in some but not all cases) but always err on the Windows/signed side.
@ -372,7 +370,7 @@ load_image (GFile *gfile, GError **error)
}
else if (bitmap_head.biSize >= 16)
{
/* all others use 32bit ints and have 4-byte table entries */
/* all others use 32bit ints and have 4-byte color table entries */
colorsize = 4;
/* BITMAPINFOHEADER / OS22XBITMAPHEADER */
@ -388,7 +386,10 @@ load_image (GFile *gfile, GError **error)
bitmap_head.biClrImp = ToL (&buffer[36]);
/* OS22XBITMAPHEADER might write garbage into mask values, but
* they will be ignored because there is no OS/2 BITFIELDS bmp */
* they will be ignored because there is no OS/2 BITFIELDS bmp.
* Likewise for the following V4 fields, which would only be used
* when the header size is larger than any valid OS/2 header.
*/
bitmap_head.masks[0] = ToL (&buffer[40]);
bitmap_head.masks[1] = ToL (&buffer[44]);
bitmap_head.masks[2] = ToL (&buffer[48]);
@ -442,10 +443,12 @@ load_image (GFile *gfile, GError **error)
{
if (bitmap_head.biCompr == BI_BITFIELDS && bitmap_head.biBitCnt == 1)
{
/* BCA_HUFFMAN1D */
bitmap_head.biCompr = BI_OS2_HUFFMAN;
}
else if (bitmap_head.biCompr == BI_JPEG && bitmap_head.biBitCnt == 24)
{
/* BCA_RLE24 */
bitmap_head.biCompr = BI_OS2_RLE24;
}
}
@ -453,7 +456,7 @@ load_image (GFile *gfile, GError **error)
if (bitmap_head.biSize <= 40 &&
(bitmap_head.biCompr == BI_BITFIELDS || bitmap_head.biCompr == BI_ALPHABITFIELDS))
{
/* BITMAPINFOHEADER stores masks right after header */
/* BITMAPINFOHEADER stores masks right after (not as part of) header */
gint nmasks;
@ -982,6 +985,8 @@ load_rle (struct Fileinfo *fi, gsize offset)
gint shift, i, j;
guchar *dest;
/* dest must be (re)calculated inside loop, because RLE can skip pixles */
while (fi->xpos <= fi->width)
{
if (! ReadOK (fi->file, fi->rowbuf, 2))