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cogl-bitmap-pixbuf: Avoid copying the buffer in more circumstances

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When loading an RGB image GdkPixbuf will pad the rowstride so that the
beginning of each row is aligned to 4 bytes. This was causing us to
fallback to the code that copies the buffer. It is probably safe to
avoid copying the buffer if we can detect that the rowstride is simply
an alignment of the packed rowstride.

This also changes the copying fallback code so that it uses the
aligned rowstride. However it is now extremely unlikely that the
fallback code would ever be used.
This commit is contained in:
Neil Roberts 2010-07-22 19:58:47 +01:00
parent fecb40a043
commit 2ccee98b31
1 changed files with 24 additions and 9 deletions
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33
cogl/cogl-bitmap-pixbuf.c
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@ -198,6 +198,7 @@ _cogl_bitmap_from_file (const char *filename,
int width; int width;
int height; int height;
int rowstride; int rowstride;
int aligned_rowstride;
int bits_per_sample; int bits_per_sample;
int n_channels; int n_channels;
guint8 *pixels; guint8 *pixels;
@ -246,12 +247,26 @@ _cogl_bitmap_from_file (const char *filename,
return FALSE; return FALSE;
} }
/* If the pixbuf is tightly packed then we can create a bitmap that /* Work out what the rowstride would be if it was packing the data
directly keeps a reference to the pixbuf to avoid copying the but aligned to 4 bytes */
data. Otherwise we need to copy because according to the aligned_rowstride = (width * n_channels + 3) & ~3;
GdkPixbuf docs we can't be sure whether the last row will be
allocated to the length of the full rowstride. */ /* The documentation for GdkPixbuf states that is not safe to read
if (rowstride == n_channels * width) all of the data as height*rowstride because the buffer might not
be allocated to include the full length of the rowstride for the
last row so arguably we should always copy the buffer when
rowstride != width*bpp because some places in Cogl assume that it
can memcpy(height*rowstride). However that rule is probably only
in place so that GdkPixbuf can implement gdk_pixbuf_new_subpixbuf
by just sharing the data and setting a large rowstride. That does
not apply in this case because we are just creating a new buffer
for a file. It seems very unlikely that GdkPixbuf would not
allocate the full rowstride in this case and it is highly
desirable to avoid copying the buffer. This instead just assumes
that whatever buffer pixbuf points into will always be allocated
to a 4-byte aligned buffer so we can avoid copying unless the
rowstride is unusually large */
if (rowstride <= aligned_rowstride)
return _cogl_bitmap_new_from_data (gdk_pixbuf_get_pixels (pixbuf), return _cogl_bitmap_new_from_data (gdk_pixbuf_get_pixels (pixbuf),
pixel_format, pixel_format,
width, width,
@ -261,14 +276,14 @@ _cogl_bitmap_from_file (const char *filename,
pixbuf); pixbuf);
pixels = gdk_pixbuf_get_pixels (pixbuf); pixels = gdk_pixbuf_get_pixels (pixbuf);
out_data = g_malloc (height * n_channels * width); out_data = g_malloc (aligned_rowstride * height);
out = out_data; out = out_data;
for (r = 0; r < height; ++r) for (r = 0; r < height; ++r)
{ {
memcpy (out, pixels, n_channels * width); memcpy (out, pixels, n_channels * width);
pixels += rowstride; pixels += rowstride;
out += n_channels * width; out += aligned_rowstride;
} }
/* Destroy GdkPixbuf object */ /* Destroy GdkPixbuf object */
@ -278,7 +293,7 @@ _cogl_bitmap_from_file (const char *filename,
pixel_format, pixel_format,
width, width,
height, height,
n_channels * width, aligned_rowstride,
(CoglBitmapDestroyNotify) g_free, (CoglBitmapDestroyNotify) g_free,
NULL); NULL);
} }