使用texelFetch()进行纹理处理 [英] texturing using texelFetch()

问题描述

当我将非最大值传递到纹理缓冲区时，在渲染时会以最大值绘制颜色的几何图形.我在使用glTexBuffer()API时发现了这个问题.

When I pass non max values into texture buffer, while rendering it draws geometry with colors at max values. I found this issue while using glTexBuffer() API.

例如假设我的纹理数据是GLubyte，当我传递小于255的任何值时，其颜色与使用255绘制的颜色相同，而不是黑色和该颜色的混合.
我尝试使用AMD和nvidia卡，但结果相同. 你能告诉我哪里出了问题吗?

E.g. Let’s assume my texture data is GLubyte, when I pass any value less than 255, then the color is same as that of drawn with 255, instead of mixture of black and that color.
I tried on AMD and nvidia card, but the results are same. Can you tell me where could be going wrong?

我将代码复制到这里:

着色器:

in vec2 a_position;
uniform float offset_x;
void main()
{ 
   gl_Position = vec4(a_position.x + offset_x, a_position.y, 1.0, 1.0);
}

碎片着色器:

out vec4 Color;
uniform isamplerBuffer sampler;
uniform int index;
void main() 
{
   Color=texelFetch(sampler,index);

}

代码:

GLubyte arr[]={128,5,250};
glGenBuffers(1,&bufferid);

glBindBuffer(GL_TEXTURE_BUFFER,bufferid);

glBufferData(GL_TEXTURE_BUFFER,sizeof(arr),arr,GL_STATIC_DRAW);
glBindBuffer(GL_TEXTURE_BUFFER,0);

glGenTextures(1, &buffer_texture);   

glBindTexture(GL_TEXTURE_BUFFER, buffer_texture);
glTexBuffer(GL_TEXTURE_BUFFER, GL_R8, bufferid);


glUniform1f(glGetUniformLocation(shader_data.psId,"offset_x"),0.0f);
glUniform1i(glGetUniformLocation(shader_data.psId,"sampler"),0);
glUniform1i(glGetUniformLocation(shader_data.psId,"index"),0);

glGenBuffers(1,&bufferid1);

glBindBuffer(GL_ARRAY_BUFFER,bufferid1);
glBufferData(GL_ARRAY_BUFFER,sizeof(vertices4),vertices4,GL_STATIC_DRAW);

attr_vertex = glGetAttribLocation(shader_data.psId, "a_position");

glVertexAttribPointer(attr_vertex, 2 , GL_FLOAT, GL_FALSE ,0, 0);

glEnableVertexAttribArray(attr_vertex);

glDrawArrays(GL_TRIANGLE_FAN,0,4);

glUniform1i(glGetUniformLocation(shader_data.psId,"index"),1);

glVertexAttribPointer(attr_vertex, 2 , GL_FLOAT, GL_FALSE ,0,(void *)(32) );

glDrawArrays(GL_TRIANGLE_FAN,0,4);

glUniform1i(glGetUniformLocation(shader_data.psId,"index"),2);

glVertexAttribPointer(attr_vertex, 2 , GL_FLOAT, GL_FALSE ,0,(void *)(64) );

glDrawArrays(GL_TRIANGLE_FAN,0,4);

在这种情况下，它会用深红色绘制所有3个正方形.

In this case it draws all the 3 squares with dark red color.

推荐答案

uniform isamplerBuffer sampler;
glTexBuffer(GL_TEXTURE_BUFFER, GL_R8, bufferid);

您的问题是:它们不匹配.

There's your problem: they don't match.

您将纹理的存储创建为无符号的8位整数，读取时将其标准化为 floats .但是您告诉着色器，您给它提供了 signed 8位整数，该整数将被读取为 integers ，而不是浮点数.

You created the texture's storage as unsigned 8-bit integers, which are normalized to floats upon reading. But you told the shader that you were giving it signed 8-bit integers which will be read as integers, not floats.

您由于不一致而混淆了OpenGL.采样器类型与纹理格式不匹配会产生不确定的行为.

You confused OpenGL by being inconsistent. Mismatching sampler types with texture formats yields undefined behavior.

应该是samplerBuffer，而不是isamplerBuffer.

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