## vector-agg-general — Anti-Grain Geometry Project. General Issues.

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Showing 2 results of 2

 [AGG] Re: adjacent shapes From: Maxim Shemanarev - 2005-09-30 15:52:56 ```Hi Patric, Yes, there is a problem. The alpha blend operation works namely in this very way, that is 0.5 over 0.5 is 0.75. It looks like you have a glass and paint with a translucent color on it. In case of translucent ink you theoretically will never achieve full opacity. And anti-aliasing is implemented namely via alpha-blending (and I don't see any other reasonable way to do so). But in certain cases it's quite possible to get rid of those adjacent edges artifacts. First, you need an RGBA buffer with premultiplied colors. Initially you clear it with rgba8(0,0,0,0) - and no other color. Then you use compositing operation "plus" instead of alpha-blend: typedef agg::comp_op_rgba_plus blender_pre_type; typedef agg::comp_adaptor_rgba blender_type; typedef agg::pixfmt_custom_blend_rgba pixfmt_type; And the restriction is that the shapes must not overlap. Then, after you render the scene you can alpha-blend the buffer over the parent layer. BTW, it can be RGB, not obligatory RGBA. But since your buffer is premultiplied, you are supposed to use a premultiplied renderer too, for example: typedef agg::pixfmt_rgba32_pre pixfmt_pre; typedef agg::renderer_base base_ren_pre_type; . . . pixfmt_pre pf_pre(rbuf_window()); base_ren_pre_type ren_base_pre(pf_pre); ren_base_pre.blend_from(image_buffer); McSeem "Patrik Jeller" wrote in message news:433CE872.1060005@... > Hi, > Unfortunately I stumbled across the issue with adjacent shapes. > On a transparent background (in the plain color space) I draw mutiple > polygons, some are connected others are not and each polygon has a > different color. The polygons do never overlap. If two polygons are > connected, instead of a smooth transition from the color of one polygon to > the color of the other I get a contour. I know this is a well known issue > and in my case it comes from a slightly drop of the alpha-channel on the > transition from one polygon to the other. > I wanted to know if there are any good work arounds? In one example > conv_contour was used but this is not possible for me I think. In an other > post I read something about using a different blending rule (0.5 + 0.5 = > 1.0 instead of 0.5 + 0.5 = 0.75). > > any help is highly appreciated. thanks. > patrik > > > > > ------------------------------------------------------- > This SF.Net email is sponsored by: > Power Architecture Resource Center: Free content, downloads, discussions, > and more. http://solutions.newsforge.com/ibmarch.tmpl ```
 [AGG] adjacent shapes From: Patrik Jeller - 2005-09-30 07:23:10 ```Hi, Unfortunately I stumbled across the issue with adjacent shapes. On a transparent background (in the plain color space) I draw mutiple polygons, some are connected others are not and each polygon has a different color. The polygons do never overlap. If two polygons are connected, instead of a smooth transition from the color of one polygon to the color of the other I get a contour. I know this is a well known issue and in my case it comes from a slightly drop of the alpha-channel on the transition from one polygon to the other. I wanted to know if there are any good work arounds? In one example conv_contour was used but this is not possible for me I think. In an other post I read something about using a different blending rule (0.5 + 0.5 = 1.0 instead of 0.5 + 0.5 = 0.75). any help is highly appreciated. thanks. patrik ```

Showing 2 results of 2