渲染倒立的场景到framebuffer

Question

我需要一些帮助渲染倒立的场景到framebuffer。我想制作镜面效果。 我有什么结果： 初始化帧缓冲：

GLuint FramebufferName = 0; 
glGenFramebuffers(1, &FramebufferName); 
glBindFramebuffer(GL_FRAMEBUFFER, FramebufferName); 

GLuint renderedTexture; 
glGenTextures(1, &renderedTexture); 
glBindTexture(GL_TEXTURE_2D, renderedTexture); 
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, SCREEN_WIDTH, SCREEN_HEIGHT, 0, GL_RGBA, GL_UNSIGNED_BYTE, 0); 
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST); 
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST); 
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); 
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE); 
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_COMPARE_FUNC, GL_LEQUAL); 
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_COMPARE_MODE, GL_COMPARE_R_TO_TEXTURE); 
glFramebufferTexture2D(GL_DRAW_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, renderedTexture, 0); 
glDrawBuffer(GL_COLOR_ATTACHMENT0); 
glReadBuffer(GL_NONE); 

绘制场景到帧缓冲器：

mView = camera.getViewMatrix(); 
    mProjection = perspective(45.0f, 4.0f/3.0f, 0.1f, 300.0f) * scale(mat4(1.0f), vec3(1.0f, -1.0f, 1.0f)); 
    glBindFramebuffer(GL_DRAW_FRAMEBUFFER, FramebufferName); 
    glViewport(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT); 
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 
    glCullFace(GL_FRONT); 
    glEnable(GL_CULL_FACE); 
    mWorld = rotate(mWorld, -15.0f, vec3(1, 0, 0)); 
    mWorld = rotate(mWorld, -30.0f, vec3(0, 1, 0)); 
    cubemap.Draw(mView, mProjection, mWorld); 
    glDisable(GL_CULL_FACE); 
    glEnable(GL_DEPTH_TEST); 
    glUseProgram(program); 
    mWorld = translate(mat4(1.0f), vec3(0, -10, 0)); 
    glUniformMatrix4fv(mvp_object, 1, GL_FALSE, value_ptr(mProjection * mView * mWorld * scale(mat4(1.0f), vec3(10.0f)))); 
    cannon.Draw(program); 

    mWorld = mat4(1.0f); 
    mWorld = translate(mat4(1.0f), vec3(50, -10, 0)); 
    mWorld = rotate(mWorld, 90.0f, vec3(0, 1, 0)); 
    glUniformMatrix4fv(mvp_object, 1, GL_FALSE, value_ptr(mProjection * mView * mWorld * scale(mat4(1.0f), vec3(10.0f)))); 
    cannon.Draw(program); 

    mWorld = mat4(1.0f); 
    mWorld = translate(mat4(1.0f), vec3(0, -10, 50)); 
    mWorld = rotate(mWorld, 140.0f, vec3(0, 1, 0)); 
    glUniformMatrix4fv(mvp_object, 1, GL_FALSE, value_ptr(mProjection * mView * mWorld * scale(mat4(1.0f), vec3(10.0f)))); 
    cannon.Draw(program); 

    glDisable(GL_DEPTH_TEST); 
    glBindFramebuffer(GL_FRAMEBUFFER, 0); 

我看到一些教程，其中使用glScalef（1.0，-1.0,1.0）到颠倒的场景。 glScalef用于旧版本的opengl。我如何在新版本的opengl中反转场景？ 对于这种效果，我已经将比例投影矩阵（mat4（1.0f），vec3（1.0，-1.0,1.0））相乘。这样对吗？

Answer 1

这是用GLSL编写的顶点着色器。

void main(void) 
{ 
    // Clean up inaccuracies 
    vec2 Pos = sign(gl_Vertex.xy); 

    gl_Position = vec4(Pos.xy, 0.0, 1.0); 
    // Image-space 
    gl_TexCoord[0].xy = vec2(-Pos.x, Pos.y) * 0.5 + 0.5; // x texture coord is inverted  
} 

Pos指筛选帧缓冲区输出对齐四边形。

片段着色器

uniform sampler2D framebufferSampler; 

void main(void) 
{ 
    gl_FragColor = texture2D(framebufferSampler, gl_TexCoord[0].xy); 
} 

屏幕对齐四可以利用顶点数组绘制

glBegin(GL_QUADS) 
{ 
    glVertex2f(-1.0f, -1.0f); 
    glVertex2f(1.0f, -1.0f); 
    glVertex2f(1.0f, 1.0f); 
    glVertex2f(-1.0f, 1.0f); 
} 
glEnd(); 

或。

GLfloat vertices[] = { 
    -1.0f, -1.0f, 
    1.0f, -1.0f, 
    1.0f, 1.0f, 
    -1.0f, 1.0f 
}; 

glEnableClientState(GL_VERTEX_ARRAY); 

glVertexPointer(2, GL_FLOAT, 0, (void*)vertices); 

glDrawArrays(GL_QUADS, 0, 4); 

glDisableClientState(GL_VERTEX_ARRAY); 

纹理，用来将挤包到四，是与先前呈现的内容（多遍着色器技术）帧缓冲器的信息。

您也可以使用其他2D纹理坐标或图像代替帧缓冲区和屏幕对齐四边形。

Original image。

倒影。

更多信息可在Learn OpenGL找到。