[cairo] State of Win32 backend?

[Owen Taylor]

On Wed, 2005-05-04 at 11:33 +0300, Tor Lillqvist wrote:
> Hi,
> 
> Cairo HEAD has for some time not built on Win32. The below makes it
> build, but I can't really say whether this is correct or not.

Thanks for looking into it. cairo-snippets is a good way to test
out the win32 backend, but unfortunately, is almost impossible to
build because you need to get libsvg/libsvg-cairo going first.

> Index: src/cairo-win32-font.c
> ===================================================================
> RCS file: /cvs/cairo/cairo/src/cairo-win32-font.c,v
> retrieving revision 1.16
> diff -p -u -4 -r1.16 cairo-win32-font.c
> --- src/cairo-win32-font.c	8 Apr 2005 20:14:17 -0000	1.16
> +++ src/cairo-win32-font.c	4 May 2005 07:30:24 -0000
> @@ -1002,20 +1002,21 @@ _cairo_win32_scaled_font_show_glyphs (vo
>      if (_cairo_surface_is_win32 (generic_surface) &&
>  	surface->format == CAIRO_FORMAT_RGB24 &&
>  	operator == CAIRO_OPERATOR_OVER &&
>  	pattern->type == CAIRO_PATTERN_SOLID &&
> -	_cairo_pattern_is_opaque (pattern)) {
> +	_cairo_pattern_is_opaque_solid (pattern)) {

This is right, but you can drop the 
pattern->type == CAIRO_PATTERN_SOLID.
 
>  	cairo_solid_pattern_t *solid_pattern = (cairo_solid_pattern_t *)pattern;
>  
>  	/* When compositing OVER on a GDI-understood surface, with a
>  	 * solid opaque color, we can just call ExtTextOut directly.
>  	 */
>  	COLORREF new_color;
>  	
> -	new_color = RGB (((int)(0xffff * solid_pattern->red)) >> 8,
> -			 ((int)(0xffff * solid_pattern->green)) >> 8,
> -			 ((int)(0xffff * solid_pattern->blue)) >> 8);
> +	/* XXX Use the unpremultiplied or premultiplied color? */
> +	new_color = RGB (((int)(0xffff * solid_pattern->color.red_short)) >> 8,
> +			 ((int)(0xffff * solid_pattern->color.green_short)) >> 8,
> +			 ((int)(0xffff * solid_pattern->color.blue_short)) >> 8);

No, this isn't right. You'll compute 0xffff * 0xffff >> 8. The 
"0xffff *" isn't needed when you are using red_short.

> Index: src/cairo-win32-surface.c
> ===================================================================
> RCS file: /cvs/cairo/cairo/src/cairo-win32-surface.c,v
> retrieving revision 1.19
> diff -p -u -4 -r1.19 cairo-win32-surface.c
> --- src/cairo-win32-surface.c	26 Apr 2005 02:38:44 -0000	1.19
> +++ src/cairo-win32-surface.c	4 May 2005 07:30:25 -0000
> @@ -532,28 +532,15 @@ _cairo_win32_surface_composite (cairo_op
>  {
>      cairo_win32_surface_t *dst = abstract_dst;
>      cairo_win32_surface_t *src;
>      cairo_surface_pattern_t *src_surface_pattern;
> -    int alpha;
>      int integer_transform;
>      int itx, ity;
>  
>      if (pattern->type != CAIRO_PATTERN_SURFACE ||
>  	pattern->extend != CAIRO_EXTEND_NONE)
>  	return CAIRO_INT_STATUS_UNSUPPORTED;
>  
> -    if (mask_pattern) {
> -	/* FIXME: When we fully support RENDER style 4-channel
> -	 * masks we need to check r/g/b != 1.0.
> -	 */
> -	if (mask_pattern->type != CAIRO_PATTERN_SOLID)
> -	    return CAIRO_INT_STATUS_UNSUPPORTED;
> -
> -	alpha = (int)(0xffff * pattern->alpha * mask_pattern->alpha) >> 8; 
> -    } else {
> -	alpha = (int)(0xffff * pattern->alpha) >> 8;
> -    }

This should be something like:

 if (mask_pattern) {
     /* FIXME: When we fully support RENDER style 4-channel
      * masks we need to check r/g/b != 1.0.
      */
    if (mask_pattern->type != CAIRO_PATTERN_SOLID)
        return CAIRO_INT_STATUS_UNSUPPORTED;

    alpha = solid_pattern->color.alpha_short >> 8;
 } else {
    alpha = 255;
 }

>  
> -    if (alpha == 255 &&
> -	src->format == dst->format &&
> -	(operator == CAIRO_OPERATOR_SRC ||
> -	 (src->format == CAIRO_FORMAT_RGB24 && operator == CAIRO_OPERATOR_OVER))) {
> -	
> -	if (!BitBlt (dst->dc,
> -		     dst_x, dst_y,
> -		     width, height,
> -		     src->dc,
> -		     src_x + itx, src_y + ity,
> -		     SRCCOPY))
> -	    return _cairo_win32_print_gdi_error ("_cairo_win32_surface_composite");
> -
> -	return CAIRO_STATUS_SUCCESS;

Don't understand why you removed this. 

>  
>  	BLENDFUNCTION blend_function;
>  
>  	blend_function.BlendOp = AC_SRC_OVER;
>  	blend_function.BlendFlags = 0;
> -	blend_function.SourceConstantAlpha = alpha;
> +	blend_function.SourceConstantAlpha = 255;

Needs to be 'alpha', see above.

>  	blend_function.AlphaFormat = src->format == CAIRO_FORMAT_ARGB32 ? AC_SRC_ALPHA : 0;
>  
>  	if (!AlphaBlend (dst->dc,
>  			 dst_x, dst_y,
> @@ -780,11 +752,12 @@ _cairo_win32_surface_set_clip_region (vo
>      }
>  }
>  
>  static cairo_int_status_t
> -_cairo_win32_get_extents (void		    *abstract_surface,
> -			  cairo_rectangle_t *rectangle)
> +_cairo_win32_surface_get_extents (void		    *abstract_surface,
> +				  cairo_rectangle_t *rectangle)
>  {
> +    cairo_win32_surface_t *surface = abstract_surface;
>      RECT clip_box;

Looks reasonable.

Regards,
						Owen

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