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OpenGL - 具有多个纹理的蒙版

发布于 2024-10-18 14:33:54 字数 259 浏览 5 评论 0原文

我根据以下概念在OpenGL中实现了遮罩：

遮罩由黑色和白色组成。
前景纹理应该仅在蒙版的白色部分可见。
背景纹理应该仅在蒙版的黑色部分可见。

我可以使用 glBlendFunc() 使白色部分或黑色部分按预期工作，但不能同时使两者工作，因为前景层不仅混合到蒙版上，而且还混合到背景层上。

有谁知道如何以最好的方式实现这一目标？我一直在网上搜索并阅读了一些有关片段着色器的内容。这是要走的路吗？

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尬尬 2024-10-25 14:33:54

这应该可行：

glEnable(GL_BLEND);
// Use a simple blendfunc for drawing the background
glBlendFunc(GL_ONE, GL_ZERO);
// Draw entire background without masking
drawQuad(backgroundTexture);
// Next, we want a blendfunc that doesn't change the color of any pixels,
// but rather replaces the framebuffer alpha values with values based
// on the whiteness of the mask. In other words, if a pixel is white in the mask,
// then the corresponding framebuffer pixel's alpha will be set to 1.
glBlendFuncSeparate(GL_ZERO, GL_ONE, GL_SRC_COLOR, GL_ZERO);
// Now "draw" the mask (again, this doesn't produce a visible result, it just
// changes the alpha values in the framebuffer)
drawQuad(maskTexture);
// Finally, we want a blendfunc that makes the foreground visible only in
// areas with high alpha.
glBlendFunc(GL_DST_ALPHA, GL_ONE_MINUS_DST_ALPHA);
drawQuad(foregroundTexture);

这相当棘手，所以如果有任何不清楚的地方请告诉我。

创建 GL 时，不要忘记请求 alpha 缓冲区语境。否则，可以获得没有 alpha 缓冲区的上下文。

编辑：在这里，我做了一个插图。

编辑：自从写下这个答案后，我了解到有更好的方法可以做到这：

如果您仅限于 OpenGL 的固定功能管道，请使用纹理环境
。如果您可以使用着色器，请使用片段着色器。

这个答案中描述的方式有效，并且在性能上并不比这两个更好的选项特别差，但不太优雅且不太灵活。

This should work:

glEnable(GL_BLEND);
// Use a simple blendfunc for drawing the background
glBlendFunc(GL_ONE, GL_ZERO);
// Draw entire background without masking
drawQuad(backgroundTexture);
// Next, we want a blendfunc that doesn't change the color of any pixels,
// but rather replaces the framebuffer alpha values with values based
// on the whiteness of the mask. In other words, if a pixel is white in the mask,
// then the corresponding framebuffer pixel's alpha will be set to 1.
glBlendFuncSeparate(GL_ZERO, GL_ONE, GL_SRC_COLOR, GL_ZERO);
// Now "draw" the mask (again, this doesn't produce a visible result, it just
// changes the alpha values in the framebuffer)
drawQuad(maskTexture);
// Finally, we want a blendfunc that makes the foreground visible only in
// areas with high alpha.
glBlendFunc(GL_DST_ALPHA, GL_ONE_MINUS_DST_ALPHA);
drawQuad(foregroundTexture);

This is fairly tricky, so tell me if anything is unclear.

Don't forget to request an alpha buffer when creating the GL context. Otherwise it's possible to get a context without an alpha buffer.

Edit: Here, I made an illustration.

Edit: Since writing this answer, I've learned that there are better ways to do this:

If you're limited to OpenGL's fixed-function pipeline, use texture environments
If you can use shaders, use a fragment shader.

The way described in this answer works and is not particularly worse in performance than these 2 better options, but is less elegant and less flexible.

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守望孤独 2024-10-25 14:33:54

Stefan Monov 的答案很好！但对于那些仍然有问题让他的答案起作用的人：

您需要检查 GLES20.glGetIntegerv(GLES20.GL_ALPHA_BITS, ib) - 您需要非零结果。
如果你得到 0 - 转到 EGLConfig 并确保传递 alpha 位
<前><代码>EGL14.EGL_RED_SIZE，8，
EGL14.EGL_GREEN_SIZE, 8,
EGL14.EGL_BLUE_SIZE, 8,
EGL14.EGL_ALPHA_SIZE, 8, <- 我没有这个并且花了很多时间
EGL14.EGL_DEPTH_SIZE, 16,

Stefan Monov's is great answer! But for those who still have issues to get his answer working:

you need to check GLES20.glGetIntegerv(GLES20.GL_ALPHA_BITS, ib) - you need non zero result.

if you got 0 - goto EGLConfig and ensure that you pass alpha bits

EGL14.EGL_RED_SIZE, 8,
EGL14.EGL_GREEN_SIZE, 8,
EGL14.EGL_BLUE_SIZE, 8,
EGL14.EGL_ALPHA_SIZE, 8, <- i havn't this and spent a much of time
EGL14.EGL_DEPTH_SIZE, 16,

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