[cairo] Blurriness when drawing from a temporary surface as the source

[Adam Richard]

Gerdus van Zyl wrote:
> The surface is probably getting scaled and thus the blurriness (if
> working with raster surface). If you want it sharp you will have to
> issue the drawing commands again or make your temp surface of the same
> resolution as the target so no scaling is needed.
>
>   
>>> whether perhaps I'm doing something suboptimal in setting up my
>>> temporary surface to pass to cairo_set_source.
>>>       
> cairo_surface_create_similar will do the right thing.
>
>   
Yeah, I was already using cairo_surface_create_similar.  If it's a 
scaling issue, I may just have to live with it - increasing the 
resolution to the same as the target would probably be too slow.  Thanks 
anyway.

> ~Gerdus
>
> On Mon, Jun 29, 2009 at 2:59 PM, Hakki Dogusan<dogusanh at tr.net> wrote:
>   
>> Hi,
>>
>> Adam Richard wrote:
>>     
>>> Hi,
>>>
>>> When I draw a shape normally, it works fine.  However, when I create a
>>> temporary surface, draw that same shape on it, then draw using the
>>> temporary surface with cairo_set_source, the image is sometimes more
>>> blurry (of lower quality) than the one drawn directly.  It is especially
>>> noticeable when drawing small shapes; not as much when drawing larger
>>> shapes.
>>>
>>> I've only noticed this blurriness in a png file resulting from
>>> write_to_png; when I write to a postscript instead it is not
>>> noticeable.  I also only notice it when I have matrix transformations
>>> set up so that the units of the shape I'm drawing are much different
>>> than device units.
>>>
>>>       
>> I may be wrong but, it may be related to:
>> FAQ: How do I draw a sharp, single-pixel-wide line?
>>
>> (I ended up adjusting all coordinates for zooming, instead of using
>> cairo_scale.)
>>
>>
>>     
>>> I've tried disabling antialiasing with cairo_set_antialias, and it does
>>> get disabled, but the 2 images are still different.
>>>
>>> Does anyone have any ideas as to what could cause an effect like this?
>>> I'm new to Cairo so I'm not sure whether it's using some approximation
>>> algorithm that could result in unavoidable blurriness in some cases, or
>>> whether perhaps I'm doing something suboptimal in setting up my
>>> temporary surface to pass to cairo_set_source.
>>>
>>>
>>>       
>> --
>> Regards,
>> Hakki Dogusan
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>>
>>     
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