alpha

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一给我里giaogiao 来源： https://www.cnblogs.com/zhulichen/p/11844463.html

先交保平安 来源： https://www.cnblogs.com/Tinor/p/11844373.html

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这是一篇神奇的博客，只有给了满分的朋友才能看见。 来源： https://www.cnblogs.com/a8-23/p/11844337.html

todo 来源： https://www.cnblogs.com/xzhcode/p/11844318.html

I want to plot my data as a dotplot using geom_point. My datapoints are overlapping, so I want to use jitter and transparency to increase visibility. Now I would also like to add a border to every datapoint to make it even more easier for the reader to see each datapoint. However, due to the alpha, it looks like my datapoints have halos around them. That's why I would like to use alpha only for the filling and alpha=0 for the border. But so far I haven't found a solution. I could plot two geom_points one being slightly larger than the other to create a border around each point with alpha=0.

I was using glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA) for alpha composing as the document said (and actually same thing was said in the Direct3D document). Everything was fine at first, until I downloaded the result from GPU and made it a PNG image. The result alpha component is wrong. Before drawing, I had cleared the frame buffer with opaque black colour. And after I drew something semi-transparent, the frame buffer became semi-transparent. Well the reason is obvious. With glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA) , we actually ignore the destination alpha channel and assume