c++ - 设置 openGL 窗口的背景图像

Question

我试图通过在正交投影矩阵上创建四边形并向其添加纹理来设置我的 openGL 窗口的背景图像。我还在我的应用程序中使用了 GLUT 工具包。

但是我有几个问题。下面是说明问题的屏幕截图:图像是灰度的，它在 x 和 y 上重复，即使纹理大小设置为与四边形相同。

这就是我要实现的目标:

这就是我得到的:

渲染和加载纹理的代码如下所示:

void orthogonalStart (void) {
    glMatrixMode(GL_PROJECTION);
    glPushMatrix();
    glLoadIdentity();
    gluOrtho2D(0, w1, 0, h1);
    glScalef(1, -1, 1);
    glTranslatef(0, -h1, 0);
    glMatrixMode(GL_MODELVIEW);
}

void orthogonalEnd (void) {
    glMatrixMode(GL_PROJECTION);
    glPopMatrix();
    glMatrixMode(GL_MODELVIEW);
}

GLuint LoadTexture( const char * filename, int width, int height )
{
    GLuint texture;
    unsigned char * data;
    FILE * file;

    //The following code will read in our RAW file
    file = fopen( filename, "rb" );
    if ( file == NULL ) return 0;
    data = (unsigned char *)malloc( width * height * 3 );
    fread( data, width * height * 3, 1, file );
    fclose( file );

    glGenTextures( 1, &texture ); 
    glBindTexture( GL_TEXTURE_2D, texture ); 
    glTexEnvf( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE ); 


    //even better quality, but this will do for now.
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,GL_LINEAR );
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER,GL_LINEAR );


    //to the edge of our shape. 
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT );
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT );

    //Generate the texture
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0,GL_RGB, GL_UNSIGNED_BYTE, data);
    free( data ); //free the texture
    return texture; //return whether it was successful
}

void FreeTexture( GLuint texture )
{
  glDeleteTextures( 1, &texture );
}

void background (void) {
    glBindTexture( GL_TEXTURE_2D, texture ); 

    orthogonalStart();

    glBegin(GL_QUADS);
        glTexCoord2d(0.0,0.0); glVertex2f(0, 0);
        glTexCoord2d(1.0,0.0); glVertex2f(1024, 0);
        glTexCoord2d(1.0,1.0); glVertex2f(1024, 1024);
        glTexCoord2d(0.0,1.0); glVertex2f(0, 1024);
        glEnd();

    orthogonalEnd();
}

void display (void) {
    glClearColor (1.0,0.0,0.0,1.0);
    glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glLoadIdentity();
    glEnable( GL_TEXTURE_2D );

    background();
    gluLookAt (0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);

    glutSwapBuffers();
}

为了将纹理从 png 转换为 Raw 格式，我使用了 photoshop，所以我认为灰度图像可能是由于转换造成的。

注意:我刚刚开始学习开放，所以这可能不是最好的方法。如果有更好的方法请告诉我

编辑:图像必须停留在一个地方而不是重新缩放

Answer 1

我会 avoid doing anything other than a glFrustum() or glOrtho() call为您的投影矩阵。

此外，如果您正在处理 3 分量像素，请将纹理加载的 GL_UNPACK_ALIGNMENT 设置为 1:

#include <GL/glut.h>

int w1 = 0;
int h1 = 0;
void reshape(int w, int h)
{
    w1 = w;
    h1 = h;
    glViewport(0, 0, w, h);
}


void orthogonalStart() 
{
    glMatrixMode(GL_PROJECTION);
    glPushMatrix();
    glLoadIdentity();
    gluOrtho2D(-w1/2, w1/2, -h1/2, h1/2);
    glMatrixMode(GL_MODELVIEW);
}

void orthogonalEnd()
{
    glMatrixMode(GL_PROJECTION);
    glPopMatrix();
    glMatrixMode(GL_MODELVIEW);
}


GLuint texture = 0;
void background()
{
    glBindTexture( GL_TEXTURE_2D, texture ); 

    orthogonalStart();

    // texture width/height
    const int iw = 500;
    const int ih = 500;

    glPushMatrix();
    glTranslatef( -iw/2, -ih/2, 0 );
    glBegin(GL_QUADS);
        glTexCoord2i(0,0); glVertex2i(0, 0);
        glTexCoord2i(1,0); glVertex2i(iw, 0);
        glTexCoord2i(1,1); glVertex2i(iw, ih);
        glTexCoord2i(0,1); glVertex2i(0, ih);
    glEnd();
    glPopMatrix();

    orthogonalEnd();
}


void display()
{
    glClearColor (1.0,0.0,0.0,1.0);
    glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glLoadIdentity();
    glEnable( GL_TEXTURE_2D );

    background();
    gluLookAt (0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);

    glutSwapBuffers();
}


GLuint LoadTexture()
{
    unsigned char data[] = { 255,0,0, 0,255,0, 0,0,255, 255,255,255 };

    glGenTextures( 1, &texture ); 
    glBindTexture( GL_TEXTURE_2D, texture ); 
    glPixelStorei( GL_UNPACK_ALIGNMENT, 1 );
    glTexEnvf( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE ); 

    //even better quality, but this will do for now.
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,GL_NEAREST);
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER,GL_NEAREST);

    //to the edge of our shape. 
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT );
    glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT );

    //Generate the texture
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 2, 2, 0,GL_RGB, GL_UNSIGNED_BYTE, data);
    return texture; //return whether it was successful
}


int main(int argc, char **argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_RGBA | GLUT_DEPTH | GLUT_DOUBLE);

    glutInitWindowSize(800,600);
    glutCreateWindow("Aspect Ratio");

    glutDisplayFunc(display);
    glutReshapeFunc(reshape);
    texture = LoadTexture();
    glutMainLoop();
    return 0;
}