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PODisplaying pixmap with glDrawPixels
 

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    <p>I've written a small example program using OpenGL and GLUT to display a 2-by-2 grid of four colored squares using the <code>glDrawPixels</code> function. Unfortunately, I've found that: </p> <ol> <li>The colors in the grid are not being displayed properly; and</li> <li>When the glPixelZoom function is passed negative arguments to rotate the pixmap, nothing is displayed in the window.</li> </ol> <p>The following C++ code snippet displays the example image. What am I doing wrong here, and what should I change to be able to view the intended colors and rotate the pixmap?</p> <pre><code> struct RGB { unsigned char r, g, b; }; class Pixmap { public: RGB color[4]; Pixmap() { color[0].r = 255; color[0].g = 0; color[0].b = 0; color[1].r = 0; color[1].g = 255; color[1].b = 0; color[2].r = 0; color[2].g = 0; color[2].b = 255; color[3].r = 255; color[3].g = 255; color[3].b = 255; } void render() { glClear(GL_COLOR_BUFFER_BIT); glDrawPixels( 2, 2, GL_RGB, GL_UNSIGNED_BYTE, color ); glFlush(); } }; // Create an instance of class Pixmap Pixmap myPixmap; void myRender() { myPixmap.render(); } int main( int argc, char *argv[] ) { int screenWidth, screenHeight; glutInit(&argc, argv); glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); screenWidth = glutGet(GLUT_SCREEN_WIDTH); screenHeight = glutGet(GLUT_SCREEN_HEIGHT); int windowWidth = screenHeight / 2; int windowHeight = screenHeight / 2; glutInitWindowSize(windowWidth, windowHeight); int posX = (screenWidth - windowWidth) / 2; int posY = (screenHeight - windowHeight) / 4; glutInitWindowPosition(posX, posY); glutCreateWindow("Picture"); GLfloat scaleX = 1.0f * windowWidth / 2; GLfloat scaleY = 1.0f * windowHeight / 2; glMatrixMode( GL_PROJECTION ); // If glPixelZoom(-scaleX, scaleY) // then no image is displayed glPixelZoom(scaleX, scaleY); glClearColor(1.0, 1.0, 1.0, 0.0); glColor3f(0.0f, 0.0f, 0.0f); glutDisplayFunc( myRender ); glutMainLoop(); } </code></pre>
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