用于片段着色器的OpenGL GLSL绑定采样器 [英] OpenGL GLSL Binding Sampler for Fragment Shader

问题描述

我希望在2D OpenGL应用程序上实现着色器。我的计划是渲染一个场景到一个framebuffer对象，然后使用着色器渲染该framebuffer对象到屏幕。

这是我画的场景一个framebuffer对象，然后从那里到屏幕。使用箭头键使月亮四处移动（我感到非常自豪！）

但是，当我尝试使用我的着色器程序渲染framebuffer对象到屏幕时， p>

这很伤心。此片段着色器是我从教程

这是Fragment着色器：

  #version 330 
 
在vec2 texCoord; 
 out vec4 outputColor; 
 
 uniform sampler2D gSampler; 
 
 void main（）
 {
 outputColor = texture2D（gSampler，texCoord）; 
} 
  

这是我如何设置统一变量：

  gSampler = glGetUniformLocation（mProgramID，gSampler）; 
 glUniform1i（gSampler，GL_TEXTURE0）; 
 

这是我如何使用我的着色器程序（mProgramID）渲染Framebuffer（fbo_texture）

  glBindFramebufferEXT（GL_FRAMEBUFFER_EXT，0）; 
 
 glUseProgram（mProgramID）; 
 glColor3f（1.0，1.0，1.0）; 
 glEnable（GL_TEXTURE_2D）; 
 
 glActiveTexture（GL_TEXTURE0 + 0）; 
 glBindTexture（GL_TEXTURE_2D，fbo_texture）; 
 
 glBegin（GL_QUADS）; x1 = 0.0; x2 = 400.0; y1 = 0.0; y2 = 400.0; 
 glTexCoord2f（0.0f，1.0f）; glVertex2f（x1，y1）; 
 glTexCoord2f（0.0f，0.0f）; glVertex2f（x1，y2）; 
 glTexCoord2f（1.0f，0.0f）; glVertex2f（x2，y2）; 
 glTexCoord2f（1.0f，1.0f）; glVertex2f（x2，y1）; 
 
 glEnd（）; glDisable（GL_TEXTURE_2D）; 
 
 SDL_GL_SwapBuffers（）; 
  

所以我的问题是 - 纹理和采样器之间的联系是什么？如果着色器已经对纹理进行采样，我需要渲染纹理的四边形吗？为什么不是只渲染一个空白的四边形，如果着色器是纹理化它？

编辑：这是顶点着色器：

  void main（）
 {
 
 gl_TexCoord [0] = gl_MultiTexCoord0; 
 gl_Position = ftransform（）; 
} 
  

解决方案

您为采样器设置统一值：

  gSampler = glGetUniformLocation（mProgramID，gSampler）; 
 glUniform1i（gSampler，GL_TEXTURE0）; 
  

您需要为制服设置的值是纹理单元的索引，而不是相应的枚举值。由于在这种情况下使用纹理单元0，您需要替换 glUniform1i（）调用：

  glUniform1i（gSampler，0）; 
  

I am hoping to implement a shader on a 2D OpenGL application. My plan is to render a scene to a framebuffer object, and then render that framebuffer object to the screen using a shader.

Here is the scene, which I have drawn to a framebuffer object, and then to the screen from there. Using the arrow keys makes the moon move around (I am quite proud of it!)

However, when I try to render the framebuffer object to the screen using my shader program, I get this:

It is very sad. This fragment shader is one which I got from a tutorial, and I'm sure the problem has to be with the Uniform Variables.

Here is the Fragment Shader:

#version 330

in vec2 texCoord;
out vec4 outputColor;

uniform sampler2D gSampler;

void main()
{
   outputColor = texture2D(gSampler, texCoord);
}

Here is how I set up the Uniform Variables:

gSampler = glGetUniformLocation(mProgramID, "gSampler");
glUniform1i(gSampler, GL_TEXTURE0);

Here is how I render the Framebuffer (fbo_texture) to the screen, using my shader program (mProgramID)

glBindFramebufferEXT(GL_FRAMEBUFFER_EXT,    0 ); 

glUseProgram(mProgramID);
glColor3f(1.0, 1.0, 1.0);
glEnable(GL_TEXTURE_2D);

glActiveTexture(GL_TEXTURE0 + 0);
glBindTexture(GL_TEXTURE_2D, fbo_texture);

glBegin(GL_QUADS);x1= 0.0;x2= 400.0;y1= 0.0;y2 = 400.0;
    glTexCoord2f(0.0f, 1.0f); glVertex2f(x1, y1);
    glTexCoord2f(0.0f, 0.0f); glVertex2f(x1, y2);
    glTexCoord2f(1.0f, 0.0f); glVertex2f(x2, y2);
    glTexCoord2f(1.0f, 1.0f); glVertex2f(x2, y1);

glEnd();glDisable(GL_TEXTURE_2D);

SDL_GL_SwapBuffers();

So my question is- What is the link between a texture and a sampler? Do I need to render a textured quad, if the shader is already sampling the texture? Why not just render a blank quad if the shader is texturizing it?

EDIT: Here is the vertex shader:

void main()
{

    gl_TexCoord[0] = gl_MultiTexCoord0;
    gl_Position = ftransform();
}

解决方案

There's indeed a problem with how you set the uniform value for the sampler:

gSampler = glGetUniformLocation(mProgramID, "gSampler");
glUniform1i(gSampler, GL_TEXTURE0);

The value you need to set for the uniform is the index of the texture unit, not the corresponding enum value. Since you are using texture unit 0 in this case, you need to replace the glUniform1i() call by:

glUniform1i(gSampler, 0);

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