OpenGL透明图像中有黑色 [英] OpenGL transparent images have black in them

问题描述

我正在为Android游戏开发游戏，我想知道为什么每当我绘制具有透明性的图像时，似乎总是在透明部分中添加了一些黑色.这种情况到处都是，使我的某些效果看起来很奇怪.

I am working on a game for Android and I was wondering why whenever I draw images with transparency there seems to always be some black added to the transparent parts. This happens all over and makes some of my effects look strange.

这里是一个例子.这两个圆圈只是带有模糊效果的白色图像，但是您可以看到一个重叠的图像带有阴影.如果我在Inkscape中重叠了两个圆圈，则重叠的地方会变成纯白色.

Here is an example. The two circles are only white images with a blur but you can see when one overlaps the other it has a shadow. If I overlap two of the circles say in Inkscape I get pure white where they overlap.

我正在使用

GLES20.glEnable(GLES20.GL_BLEND);
GLES20.glBlendFunc(GLES20.GL_SRC_ALPHA, GLES20.GL_ONE_MINUS_SRC_ALPHA);

用于我的混合.

您知道为什么会发生这种情况以及如何避免这种情况吗?

Any idea why this happens and how I can avoid it?

我唯一能想到的是两个图像具有相同的z，所以也许它们仅与背景混合而不是彼此混合?

the only thing I can think of is that the two images have the same z so maybe they are blending only with the background instead of each other?

我改变了

GLES20.glBlendFunc(GLES20.GL_SRC_ALPHA, GLES20.GL_ONE_MINUS_SRC_ALPHA);

到

GLES20.glBlendFunc(GLES20.GL_SRC_ALPHA, GLES20.GL_DST_ALPHA);

这是我想要的结果.

现在唯一的是我所拥有的透明图像中有黑色的透明图像被忽略了，这是有道理的，因为我认为目标alpha为1.为什么一个负源会添加该灰色?

The only thing now is that the transparent images that I had that have a transparent black in them are ignored, which makes sense because I think the destination alpha is 1. Why would One minus source add that gray?

推荐答案

我想出了解决方法.

我改变了

GLES20.glBlendFunc(GLES20.GL_SRC_ALPHA, GLES20.GL_ONE_MINUS_SRC_ALPHA);

到

GLES20.glBlendFunc(GLES20.GL_ONE, GLES20.GL_ONE_MINUS_SRC_ALPHA);

事实证明，Android在加载时会预先乘以PNG图像的纹理Alpha(使白色变为灰色).

It turns out that Android pre-multiplies the alpha of textures of PNG images when you load it (making white turn gray).

我添加了

vColor.r = vColor.r * vColor.a;
vColor.g = vColor.g * vColor.a;
vColor.b = vColor.b * vColor.a;

向我的顶点着色器进行其他颜色的乘法.

to my vertex shader to do the multiplying for my other colors.

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