如何在 iPhone 上的 OpenGL ES 2.0 中混合具有不同坐标的两个纹理? [英] How do I blend two textures with different co-ordinates in OpenGL ES 2.0 on iPhone?
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具有不同混合模式的两个纹理.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)
我知道该怎么做...
但不知道该怎么做……
为了在一个矩形(第一张图片)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...
attribute vec4 position;
attribute vec4 inputTextureCoordinate;
varying vec2 textureCoordinate;
void main()
{
gl_Position = position;
textureCoordinate = inputTextureCoordinate.xy;
}
片段着色器...
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
你必须将2个纹理坐标传递给shader并修改shader
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);
顶点着色器
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;
}
片段着色器
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);
}
顺便说一句,inputTextureCoordinate 不一定是 vec4,但它可以是 vec2
BTW inputTextureCoordinate is not necessary to be vec4 but it could be vec2
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