紋理不適合在廣場 - OpenGL

Question

我想創建一個廣場，並把它放在一個紅色的圓圈。正如你可以在簡單VERT我見地圖（-1,1）至（0,1）範圍：

coord = position.xy*0.5 + vec2(0.5,0.5); 

如果你看一下simple.frag，有這樣一行：

if(abs(length(coord - vec2(0.5,0.5))) < 0.3) 

因此，我期待在廣場中間的紅圈。然而這種情況：

圓的中心是超出（0.5，0.5）。如果我把上面一行是：

if(abs(length(coord - vec2(0.0,0.0))) < 0.3) 

輸出是：

圓的中心位於左下角預期。但是不應該是右上角（1,1）？圓也不是完美的圓。我錯過了什麼？

初始化：

Shader simpleShader("simple.vert", "simple.frag"); 
Shader quadShader("quad.vert", "quad.frag"); 


GLfloat inVertices[] = { 

    -1.0f, 1.0f, 0.0, 
    -1.0f, -1.0f, 0.0, 
    1.0f, -1.0f, 0.0, 

    -1.0f, 1.0f, 0.0, 
    1.0f, -1.0f, 0.0, 
    1.0f, 1.0f, 0.0 }; 


GLfloat quadVertices[] = { 

    -1.0f, 1.0f, 0.0f, 0.0f, 1.0f, 
    -1.0f, -1.0f, 0.0f, 0.0f, 0.0f, 
    1.0f, -1.0f, 0.0f, 1.0f, 0.0f, 

    -1.0f, 1.0f, 0.0f, 0.0f, 1.0f, 
    1.0f, -1.0f, 0.0f, 1.0f, 0.0f, 
    1.0f, 1.0f, 0.0f, 1.0f, 1.0f 
}; 


GLuint inVAO, inVBO; 
glGenVertexArrays(1, &inVAO); 
glGenBuffers(1, &inVBO); 
glBindVertexArray(inVAO); 
glBindBuffer(GL_ARRAY_BUFFER, inVBO); 
glBufferData(GL_ARRAY_BUFFER, sizeof(inVertices), &inVertices, GL_STATIC_DRAW); 
glEnableVertexAttribArray(0); 
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, (GLvoid*)0); 
glBindVertexArray(0); 


GLuint quadVAO, quadVBO; 
glGenVertexArrays(1, &quadVAO); 
glGenBuffers(1, &quadVBO); 
glBindVertexArray(quadVAO); 
glBindBuffer(GL_ARRAY_BUFFER, quadVBO); 
glBufferData(GL_ARRAY_BUFFER, sizeof(quadVertices), &quadVertices, GL_STATIC_DRAW); 
glEnableVertexAttribArray(0); 
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(GLfloat), (GLvoid*)0); 
glEnableVertexAttribArray(1); 
glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 5 * sizeof(GLfloat), (GLvoid*)(3 * sizeof(GLfloat))); 
glBindVertexArray(0); 





GLuint textureColorbuffer; 
glGenTextures(1, &textureColorbuffer); 
glBindTexture(GL_TEXTURE_2D, textureColorbuffer); 
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 256, 256, 0, GL_RGB, GL_UNSIGNED_BYTE, NULL); 
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); 
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); 
glBindTexture(GL_TEXTURE_2D, 0); 

GLuint framebuffer; 
glGenFramebuffers(1, &framebuffer); 
glBindFramebuffer(GL_FRAMEBUFFER, framebuffer); 
// Create a color attachment texture 
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, textureColorbuffer, 0); 
if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) 
    std::cout << "ERROR::FRAMEBUFFER:: Framebuffer is not complete!" << std::endl; 
glBindFramebuffer(GL_FRAMEBUFFER, 0); 

主迴路;

glBindFramebuffer(GL_FRAMEBUFFER, framebuffer); 
    glClearColor(0.2f, 0.3f, 0.3f, 1.0f); 
    glClear(GL_COLOR_BUFFER_BIT); 

    // Draw our first triangle 
    simpleShader.Use(); 
    glBindVertexArray(inVAO); 
    glDrawArrays(GL_TRIANGLES, 0, 6); 

    glBindVertexArray(0); 
    glBindFramebuffer(GL_FRAMEBUFFER, 0); 


    glClearColor(0.0f, 0.0f, 0.0f, 1.0f); 
    glClear(GL_COLOR_BUFFER_BIT); 
    quadShader.Use(); 
    modelLoc = glGetUniformLocation(quadShader.Program, "model"); 
    viewLoc = glGetUniformLocation(quadShader.Program, "view"); 
    projLoc = glGetUniformLocation(quadShader.Program, "projection"); 
    glUniformMatrix4fv(modelLoc, 1, GL_FALSE, glm::value_ptr(model)); 
    glUniformMatrix4fv(viewLoc, 1, GL_FALSE, glm::value_ptr(view)); 
    glUniformMatrix4fv(projLoc, 1, GL_FALSE, glm::value_ptr(projection)); 

    glBindVertexArray(quadVAO); 
    glBindTexture(GL_TEXTURE_2D, textureColorbuffer); // Use the color attachment texture as the texture of the quad plane 
    glDrawArrays(GL_TRIANGLES, 0, 6); 
    glBindVertexArray(0); 

    // Swap the screen buffers 
    glfwSwapBuffers(window); 

simple.vert：

#version 330 core 

layout (location = 0) in vec3 position; 
out vec2 coord; 
void main(){ 
    coord = position.xy*0.5 + vec2(0.5,0.5); 
    gl_Position = vec4(position, 1.0f); 
} 

simple.frag：

#version 330 core 
in vec2 coord; 
out vec4 color; 
void main(){ 
    if(abs(length(coord - vec2(0.5,0.5))) < 0.3) 
     color = vec4(1.0f, 0.0f, 0.0f, 1.0f); 
    else 
     color = vec4(0.0f, 1.0f, 0.0f, 1.0f); 
} 

quad.vert：

#version 330 core 
layout (location = 0) in vec3 position; 
layout (location = 1) in vec2 texCoords; 
uniform mat4 model; 
uniform mat4 view; 
uniform mat4 projection; 
out vec2 TexCoords; 

void main() 
{ 
    gl_Position = projection * view * model * vec4(position, 1.0f); 
    TexCoords = texCoords; 
} 

quad.frag：

#version 330 core 
in vec2 TexCoords; 
out vec4 color; 

uniform sampler2D screenTexture; 

void main() 
{ 
    color = texture(screenTexture, TexCoords); 
} 

Answer 1

繪製到紋理時，必須修改視口。如果使用窗口的視口，OpenGL會假定紋理與窗口大小相同。因此，只有整個圖像的左下角纔會出現在紋理中。

所以渲染到紋理之前：

glViewport(0, 0, 256, 256); 

...並恢復該畫最終的現場。