解决OpenGL浮点精度输出问题：深度解析与Framebuffer对象应用

#version 330 core
out vec4 out_color;
in vec2 fTexcoords;

void main() {
    vec4 tempcolor = vec4(0.0);
    float ran = 0.003921568627451; // 约 1/255
    for(int i = 0;i < 100;i++) {
        tempcolor = tempcolor + ran * ran; // ran*ran 约 1.5378e-5
    }
    out_color = tempcolor; // 最终 tempcolor 约 0.00153787
}

import numpy as np
tempcolor_cpu = np.array([0.], dtype='float32')
ran_cpu = 0.003921568627451
for i in range(100):
    tempcolor_cpu = tempcolor_cpu + ran_cpu * ran_cpu
print(tempcolor_cpu) # 输出: [0.00153787]

import OpenGL.GL as GL
from OpenGL.GL import *
import numpy as np
import ctypes

# 假设已经完成了OpenGL上下文的初始化、顶点缓冲对象(VBO)、
# 元素缓冲对象(EBO)以及顶点数组对象(VAO)的设置。
# 并且已经创建了着色器程序并链接。

# 顶点着色器 (与原问题相同)
vertex_src = """
#version 330 core
in vec3 a_position;
in vec2 vTexcoords;
out vec2 fTexcoords;
void main() {
    gl_Position = vec4(a_position, 1.0);
    fTexcoords = vTexcoords;
}
"""

# 片段着色器 (与原问题相同)
fragment_src = """
#version 330 core
out vec4 out_color;
in vec2 fTexcoords;

void main() {
    vec4 tempcolor = vec4(0.0);
    float ran = 0.003921568627451;
    for(int i = 0;i < 100;i++)
        tempcolor = tempcolor + ran*ran;

    out_color = tempcolor;
}
"""

# ... OpenGL初始化代码 ...
# (例如，创建窗口，设置视口，编译链接着色器等)

# 假设shaderProgram是已编译链接的着色器程序ID
# 假设vertices和indices是定义了绘制几何体的数组
# 假设VAO已经绑定并配置好

# 1. 创建并配置FBO
fbo = glGenFramebuffers(1)
glBindFramebuffer(GL_FRAMEBUFFER, fbo)

# 2. 创建一个浮点纹理作为FBO的颜色附件
texture_width, texture_height = 1280, 720 # 与glReadPixels读取尺寸一致
color_texture = glGenTextures(1)
glBindTexture(GL_TEXTURE_2D, color_texture)
# 指定纹理的内部格式为GL_RGBA32F，表示每个通道32位浮点数
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA32F, texture_width, texture_height, 0, GL_RGBA, GL_FLOAT, None)
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR)
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR)
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE)
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE)

# 3. 将纹理附加到FBO的颜色附件0
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, color_texture, 0)

# (可选) 如果需要深度/模板测试，可以附加一个深度/模板渲染缓冲区或纹理
# depth_stencil_rb = glGenRenderbuffers(1)
# glBindRenderbuffer(GL_RENDERBUFFER, depth_stencil_rb)
# glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH24_STENCIL8, texture_width, texture_height)
# glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_STENCIL_ATTACHMENT, GL_RENDERBUFFER, depth_stencil_rb)

# 4. 检查FBO完整性
if glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE:
    print("Error: Framebuffer is not complete!")
    # 根据实际情况处理错误，例如退出程序

# 设置视口以匹配FBO纹理尺寸
glViewport(0, 0, texture_width, texture_height)

# 5. 渲染到FBO
glClearColor(0.0, 0.0, 0.0, 1.0) # 清除颜色（FBO的背景色）
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT) # 清除FBO的颜色和深度缓冲区

glUseProgram(shaderProgram) # 使用着色器程序
# ... 设置顶点属性，绑定VAO等 ...
glDrawElements(GL_TRIANGLES, len(indices), GL_UNSIGNED_SHORT, None) # 绘制几何体

# 6. 从FBO读取像素
# 保持FBO绑定，或者在读取前重新绑定FBO
# glBindFramebuffer(GL_FRAMEBUFFER, fbo) # 如果之前解绑了，需要重新绑定
buffer = glReadPixels(0, 0, texture_width, texture_height, GL_RGBA, GL_FLOAT, None)

# 打印读取到的像素值 (例如，中间一个像素)
# 注意：PyOpenGL的glReadPixels返回的是一个扁平的numpy数组
# 需要根据宽度、高度和通道数进行重塑
buffer_reshaped = buffer.reshape(texture_height, texture_width, 4) # RGBA
print(buffer_reshaped[1][1]) # 打印 (1,1) 处的像素值

# 期望输出类似: [0.00153787 0.00153787 0.00153787 0.00000000] (因为我们用RGBA32F，但只写了RGB)

# 7. 清理FBO资源
glDeleteFramebuffers(1, [fbo])
glDeleteTextures(1, [color_texture])
# glDeleteRenderbuffers(1, [depth_stencil_rb]) # 如果创建了深度/模板渲染缓冲区

# 恢复默认帧缓冲区进行后续渲染或显示
glBindFramebuffer(GL_FRAMEBUFFER, 0)
# 恢复默认视口
# glViewport(0, 0, window_width, window_height)