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[cairo-image-surface.c] Cleanup stride checking and improve docs

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This commit is contained in:
Behdad Esfahbod 2008-01-29 00:42:51 -05:00
parent 8e3250b856
commit 013781137f
1 changed files with 8 additions and 8 deletions
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16
src/cairo-image-surface.c
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@ -394,6 +394,9 @@ _cairo_image_surface_create_with_content (cairo_content_t content,
width, height);
}
/* pixman required stride alignment in bytes. should be power of two. */
#define STRIDE_ALIGNMENT (sizeof (uint32_t))
/**
* cairo_format_stride_for_width:
* @format: A #cairo_format_t value
@ -425,10 +428,7 @@ cairo_format_stride_for_width (cairo_format_t format,
{
int bpp = _cairo_format_bits_per_pixel (format);
/* Convert from bits-per-row to bytes-per-row with rounding to the
* next 4-byte boundary. This satisifies the current alignment
* requirements of pixman. */
return (((bpp * width) + 31) >> 5) << 2;
return ((bpp*width+7)/8 + STRIDE_ALIGNMENT-1) & ~(STRIDE_ALIGNMENT-1);
}
/**
@ -451,9 +451,9 @@ cairo_format_stride_for_width (cairo_format_t format,
* must explicitly clear the buffer, using, for example,
* cairo_rectangle() and cairo_fill() if you want it cleared.
*
* Note that the stride will often be larger than
* width*bytes_per_pixel to provide proper alignment for each
* row. This alignment is required to allow high-performance rendering
* Note that the stride may be larger than
* width*bytes_per_pixel to provide proper alignment for each pixel
* and row. This alignment is required to allow high-performance rendering
* within cairo. The correct way to obtain a legal stride value is to
* call cairo_format_stride_for_width() with the desired format and
* maximum image width value, and the use the resulting stride value
@ -486,7 +486,7 @@ cairo_image_surface_create_for_data (unsigned char *data,
if (! CAIRO_FORMAT_VALID (format))
return _cairo_surface_create_in_error (_cairo_error(CAIRO_STATUS_INVALID_FORMAT));
if (stride % sizeof (uint32_t) != 0)
if ((stride & (STRIDE_ALIGNMENT-1)) != 0)
return _cairo_surface_create_in_error (_cairo_error (CAIRO_STATUS_INVALID_STRIDE));
pixman_format = _cairo_format_to_pixman_format_code (format);