问题
i have a question about achieving an effect like on a lunar eclipse. The effect should look like in the first seconds of this gif. So just like a black shadow which goes over the circle. The ideal situation would be a function where i can passed a parameter in percentage to get this amount as a shadow on the circle:
The problem which i am facing is that my background is an gradient. So it's not possible to have a black circle which moves over the moon to get the effect.
I tried something with CCClippingNode but it looks not nice. Furthermore the clip on the edges was always a bit pixelated.
I thought about using something like a GLSL Shader to achieve the effect but i am not so familiar with GLSL and i can't find an example.
The effect is for an app game developed for an iphone. I use the cocos2d framework in version 3 (the current one).
Has somebody an idea how to get this effect? An idea where i can start to search?
Thank you in advance
回答1:
The physics behind is simple you change the light shining on the moon. So
I would create a 1D gradient texture representing the lighting conditions
compute each rendered pixel of moon
you obviously have the 2D texture of moon. So you now need to obtain the position of each pixel inside the 1D lighting texture. So if moon is fully visible you are in sunlight. When partially eclipsed then you are in the umbra region. And finaly while total eclipse you are in penumbra region. so just compute the middle point's of the moon position. And for the rest use relative position in the moons motion direction.
So now just multiply the Moon surface with the lighting texture and render the output.
when working you can add the curvature correction
Now you got linerly cutted Moon phases but the real phases are curved as the lighting conditions differs also with radial distance from motion direction and moons center. To fix this you can do
- convert the lighting to 2D texture
- or shift the texture coordinate by some curvature dependent on the radial distance
来源：https://stackoverflow.com/questions/33258872/cocos2d-lunar-eclipse-effect-on-iphone