如何在iPhone上的OpenGL ES 2.0中混合使用不同坐标的两个纹理？

问题描述

当两个纹理覆盖相同的矩形时，我可以在片段着色器中混合两个具有不同混合模式的纹理。但现在我的问题是，一个纹理是一个没有旋转的普通矩形，另一个纹理是另一个具有旋转/缩放和平移的矩形。如何以我想要的方式合并这些纹理？ （图片中）

I can blend two textures with different blending modes in the fragment shader when both the textures covers the same rectangles. But now my problem is, one texture is a plain rectangle with no rotation and the other texture is another rectangle with a rotation/scale and translation. How do I merge these textures in the way I want? (In the picture)

我知道怎么做...

但不确定如何执行此操作...

But not sure how to do this...

为了在一个矩形（第一个图像）中混合纹理，我使用了以下代码..

For blending textures in one rectangle (the first image), I used the following code..

目标C代码...

- (void) display {
    [EAGLContext setCurrentContext:context];

    glBindFramebuffer(GL_FRAMEBUFFER, targetFBO);

    glUseProgram(program);

    glActiveTexture(GL_TEXTURE2);
    glBindTexture(GL_TEXTURE_2D, textureTop);

    glActiveTexture(GL_TEXTURE3);
    glBindTexture(GL_TEXTURE_2D, textureBot);

    glUniform1i(inputTextureTop, 2);
    glUniform1i(inputTextureBot, 3);

    glUniform1f(alphaTop, alpha);

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

    glVertexAttribPointer(position, 2, GL_FLOAT, 0, 0, imageVertices);
    glVertexAttribPointer(inputTextureCoordinate, 2, GL_FLOAT, 0, 0, textureCoordinates);

    glClearColor(0.0, 0.0, 0.0, 0.0);
    glClear(GL_COLOR_BUFFER_BIT);

    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

    glBindRenderbuffer(GL_RENDERBUFFER, viewRenderbuffer);
    [context presentRenderbuffer:GL_RENDERBUFFER];
}

顶点着色器......

Vertex shader...

 attribute vec4 position;
 attribute vec4 inputTextureCoordinate;

 varying vec2 textureCoordinate;

 void main()
 {
    gl_Position = position;
    textureCoordinate = inputTextureCoordinate.xy;
 }

片段着色器......

Fragment shader...

varying highp vec2 textureCoordinate;

uniform sampler2D inputTextureTop;
uniform sampler2D inputTextureBot;

uniform highp float alphaTop;

void main()
{
    lowp vec4 pixelTop = texture2D(inputTextureTop, textureCoordinate);
    lowp vec4 pixelBot = texture2D(inputTextureBot, textureCoordinate);

    gl_FragColor = someBlendOperation(pixelTop, pixelBot);
}

推荐答案

你必须传递2个纹理坐标到着色器和修改着色器

You have to pass 2 texture coordinates to shader and modify shader

添加到ObjectiveC

Add to ObjectiveC

glVertexAttribPointer(inputTextureCoordinate2, 2, GL_FLOAT, 0, 0, textureCoordinates2);

Vertex Shader

Vertex Shader

attribute vec4 position;
attribute vec4 inputTextureCoordinate;
attribute vec4 inputTextureCoordinate2;

varying vec2 textureCoordinate;
varying vec2 textureCoordinate2;

void main()
{
    gl_Position = position;
    textureCoordinate = inputTextureCoordinate.xy;
    textureCoordinate2 = inputTextureCoordinate2.xy;
}

Frag Shader

Frag Shader

varying highp vec2 textureCoordinate;
varying highp vec2 textureCoordinate2;

uniform sampler2D inputTextureTop;
uniform sampler2D inputTextureBot;

uniform highp float alphaTop;

void main()
{
    lowp vec4 pixelTop = texture2D(inputTextureTop, textureCoordinate);
    lowp vec4 pixelBot = texture2D(inputTextureBot, textureCoordinate2);

    gl_FragColor = someBlendOperation(pixelTop, pixelBot);
}

BTW inputTextureCoordinate不一定是vec4但它可能是vec2

BTW inputTextureCoordinate is not necessary to be vec4 but it could be vec2

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