Re: Drawing antialiased shapes with alpha transparency

[ERDI Gergo <cactus cactus rulez org>]

On Sat, 8 Jan 2005, Samuel Abels wrote:

> I also tried using
>
>  Gdk::Window::draw_rgb_32_image(gc,
>                                 x, y, width, height,
>                                 Gdk::RGB_DITHER_NONE,
>                                 buffer,
>                                 stride);
>
> but this API does not allow to copy only an area (x1, y1, x2, y2) of the
> source buffer to the widget's buffer (x3, y3), so I would have to create
> another temporary image. If I don't, this is very slow (there is a
> flicker).

well, with a clever rowstride you can solve this. let's say orig_buffer is 
sized w x h, and each pixel takes up 4 bytes. You want to render (x, y, 
view_w, view_h). So you can do

new_buffer = orig_buffer + (y * orig_rowstride) + (x * 4);
win.draw_rgb_image (gc, x, y, view_w, view_h, Gdk::RGB_DITHER_NONE,
		    new_buffer, orig_rowstride);

(I don't have the faintest idea what you're actually doing (never looked 
at Cairo), just pointing out how you can avoid copying the buffer to 
render sub-regions of it)

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