c++ - opengl Framebuffer offscreen 到纹理，颜色错误

Question

我正在尝试使用帧缓冲区来离屏渲染立方体。然后我尝试使用它的纹理将它转换为纹理。我遇到的问题是当我尝试将该纹理放在平面上时。纹理颜色完全基于一种原色:芦苇、绿色或蓝色。我不知道问题出在哪里，也许是从 float 到 double 的转换问题？我真的不知道该想什么或去哪里探索。

这是我得到的 gif。在此 gif 中，您可以看到没有离屏渲染的普通立方体。第二个绿色立方体是打印在平面上的帧缓冲区的纹理:

这是我使用的代码。它基于 Qt，但与过剩没有区别。我解释它是为了更容易理解:

1. initializeGL:我声明帧缓冲区及其附件
2. PaintGL:如果我不“左键单击”以启用此功能，则无需使用 FB 即可绘制立方体(gif 的第一部分，效果完美)。如果我左键单击，那么例程会更改并在 FrameBuffer 上绘制立方体，然后我在平面上绘制它的纹理。 (gif 的第二部分，它将我的纹理涂成绿色)
3. setProyection:设置普通立方体绘制的 glOrtho。

#include "WidgetOpenGL.h"

WidgetOpenGL::WidgetOpenGL(QWidget *parent) : QOpenGLWidget(parent)
{

}

void WidgetOpenGL::initializeGL()
{
    desplazamientoX = 1;
    desplazamientoY = 0;
    initializeOpenGLFunctions();
    glClearColor(0.0, 0.0, 0.0, 0.0);
    glEnable(GL_DEPTH_TEST);
    buttonpressed = false;
    glGenFramebuffers(1, &buffer);
    glBindFramebuffer(GL_FRAMEBUFFER, buffer);
    glGenTextures(1, &renderedTexture);
    glBindTexture(GL_TEXTURE_2D, renderedTexture);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 1024, 768, 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);
    glGenRenderbuffers(1, &renderedDepth);
    glBindRenderbuffer(GL_RENDERBUFFER, renderedDepth);
    glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT, 1024, 768);
    glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, renderedDepth);
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, renderedTexture, 0);
    glBindFramebuffer(GL_FRAMEBUFFER, 0);
    setProyection();
    setModelView();
}

void WidgetOpenGL::paintGL()
{
    if (buttonpressed)
    {
        glBindFramebuffer(GL_FRAMEBUFFER, buffer);
        glViewport(0, 0, 1024, 768);
    }
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    setProyection();
    setModelView();
    glTranslatef(0.0, 0.0, -2.0);
    setRotation();

    glBegin(GL_QUADS);
    // top
    glColor3f(1.0f, 0.0f, 0.0f);
    glNormal3f(0.0f, 1.0f, 0.0f);
    glVertex3f(-0.5f, 0.5f, 0.5f);
    glVertex3f(0.5f, 0.5f, 0.5f);
    glVertex3f(0.5f, 0.5f, -0.5f);
    glVertex3f(-0.5f, 0.5f, -0.5f);

    glEnd();

    glBegin(GL_QUADS);
    // front
    glColor3f(0.0f, 1.0f, 0.0f);
    glNormal3f(0.0f, 0.0f, 1.0f);
    glVertex3f(-0.5f, -0.5f, 0.5f);
    glVertex3f(0.5f, -0.5f, 0.5f);
    glVertex3f(0.5f, 0.5f, 0.5f);
    glVertex3f(-0.5f, 0.5f, 0.5f);

    glEnd();

    glBegin(GL_QUADS);
    // right
    glColor3f(0.0f, 0.0f, 1.0f);
    glNormal3f(1.0f, 0.0f, 0.0f);
    glVertex3f(0.5f, -0.5f, 0.5f);
    glVertex3f(0.5f, -0.5f, -0.5f);
    glVertex3f(0.5f, 0.5f, -0.5f);
    glVertex3f(0.5f, 0.5f, 0.5f);

    glEnd();

    glBegin(GL_QUADS);
    // left
    glColor3f(0.0f, 0.0f, 0.5f);
    glNormal3f(-1.0f, 0.0f, 0.0f);
    glVertex3f(-0.5f, -0.5f, 0.5f);
    glVertex3f(-0.5f, 0.5f, 0.5f);
    glVertex3f(-0.5f, 0.5f, -0.5f);
    glVertex3f(-0.5f, -0.5f, -0.5f);

    glEnd();

    glBegin(GL_QUADS);
    // bottom
    glColor3f(0.5f, 0.0f, 0.0f);
    glNormal3f(0.0f, -1.0f, 0.0f);
    glVertex3f(-0.5f, -0.5f, 0.5f);
    glVertex3f(0.5f, -0.5f, 0.5f);
    glVertex3f(0.5f, -0.5f, -0.5f);
    glVertex3f(-0.5f, -0.5f, -0.5f);

    glEnd();

    glBegin(GL_QUADS);
    // back
    glColor3f(0.0f, 0.5f, 0.0f);
    glNormal3f(0.0f, 0.0f, -1.0f);
    glVertex3f(0.5f, 0.5f, -0.5f);
    glVertex3f(0.5f, -0.5f, -0.5f);
    glVertex3f(-0.5f, -0.5f, -0.5f);
    glVertex3f(-0.5f, 0.5f, -0.5f);

    glEnd();
    glFlush();

    if (buttonpressed)
    {
        glBindFramebuffer(GL_FRAMEBUFFER, 0);
        //      QImage img = frameBuffer->toImage();
        //      img.save("Hola.jpg");

        //draw plane with texture
        setViewport();
        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        glOrtho(-2.0, 2.0, -2.0, 2.0, -2.0, 2.0);
        glMatrixMode(GL_MODELVIEW);
        glLoadIdentity();
        glClearColor(0.1f, 0.1f, 0.1f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        glEnable(GL_TEXTURE_2D);
        glBindTexture(GL_TEXTURE_2D, renderedTexture);
        glBegin(GL_QUADS);
        glTexCoord2d(0.0f, 0.0f);
        glVertex3f(-1.0, -1.0, -1.0);
        glTexCoord2d(1.0f, 0.0f);
        glVertex3f(1.0, -1.0, -1);
        glTexCoord2d(1.0f, 1.0f);
        glVertex3f(1.0, 1.0, -1.0);
        glTexCoord2d(0.0f, 1.0f);
        glVertex3f(-1.0, 1.0, -1.0);
        glEnd();
        glBindTexture(GL_TEXTURE_2D, 0);
        glDisable(GL_TEXTURE_2D);
        glFlush();
    }
}

void WidgetOpenGL::resizeGL(int w, int h)
{
    setViewport();
    setProyection();
    setModelView();
}

void WidgetOpenGL::setViewport()
{
    int ancho = this->width();
    int alto = this->height();
    glViewport(0, 0, ancho, alto);
}

void WidgetOpenGL::setProyection()
{
    int ancho = this->width();
    int alto = this->height();
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(-1.0, 1.0, -1.0, 1.0, -1.0, 10.0);
    //gluPerspective(90.0f, ancho / (GLdouble)alto, 0.0f, 10.0f);
}

void WidgetOpenGL::setModelView()
{
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}

void WidgetOpenGL::mouseMoveEvent(QMouseEvent *event)
{
    desplazamientoY += ((event->x() - initX) * 360) / (GLdouble)width();
    desplazamientoX += ((event->y() - initY) * 360) / (GLdouble)height();
    initX = event->x();
    initY = event->y();

    if (((int)desplazamientoX % 360) == 0) desplazamientoX = 0;
    if (((int)desplazamientoY % 360) == 0) desplazamientoY = 0;
    repaint();

}

void WidgetOpenGL::mousePressEvent(QMouseEvent *event)
{
    if (event->button() == Qt::LeftButton)
    {
        initX = event->x();
        initY = event->y();
    }
    else
    {
        buttonpressed = !buttonpressed;
        repaint();
    }
}

void WidgetOpenGL::setRotation()
{
    glRotatef(desplazamientoX, 1.0, 0.0, 0.0);
    glRotatef(desplazamientoY, 0.0, 1.0, 0.0);
}

如果需要，这里是头文件:

#ifndef WIDGETOPENGL_H
#define WIDGETOPENGL_H
#include <QtWidgets/QMainWindow>
#include <QtWidgets/qopenglwidget.h>
#include <QtOpenGL>
#include <GL/GLU.h>


class WidgetOpenGL : public QOpenGLWidget, protected QOpenGLFunctions
{
    Q_OBJECT

public:
    WidgetOpenGL(QWidget *parent);

signals:
    void screenClicked();
protected:
    void initializeGL();
    void paintGL();
    void resizeGL(int w, int h);

    void setViewport();
    void setProyection();
    void setModelView();

private:
    int initX;
    int initY;
    QOpenGLFramebufferObject *frameBuffer;
    GLuint buffer;
    GLuint renderedTexture;
    GLuint renderedDepth;
    bool buttonpressed;
    QImage image;
    GLdouble desplazamientoX;
    GLdouble desplazamientoY;
    void setRotation();
    void mouseMoveEvent(QMouseEvent *event);
    void mousePressEvent(QMouseEvent *event);

};

#endif

Answer 1

解决了!问题是我在绿色平面上绘制纹理。那是因为最后一个 glcolor3f 是绿色的(当我绘制真实立方体的背板时使用)。

我只需要在绘制平面之前添加 glColor3f(1.0,1.0,1.0) 即可制作一个白色平面。