OpenGL, unusual artifacts on rendered texture, render co-ordinates?

Question

I am trying to render a simple quad to perfectly cover the screen (one to one replication). The texture I am using to render was captured from a previous render using a framebuffer and glGetTexImage. This part I'm fine with. However when I load and display the texture again I get some odd artifacts in the render (top left corner) and so far I have been unable to get rid of them.

For comparison this is what it currently looks like:

And this is what it should look like:

This maybe due to texture co-ordinates, screen co-ordinates but everything I have so far tried has failed. What should I change/do differently?

Rendering code follows.

void setWidthHeightRender(GLsizei width, GLsizei height) {
    if(height == 0)
        height = 1;

    glViewport(0, 0, width, height);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    //GLdouble left, GLdouble right, GLdouble bottom, GLdouble top, GLdouble zNear, GLdouble zFar
    glOrtho(0.0, width, height, 0.0, -1.0, 1.0);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}
unsigned createGLTexture(unsigned width, unsigned height, const uint8_t* data) {
    // the texture we're going to render
    GLuint renderedTexture;
    glGenTextures(1, &renderedTexture);

    // bind the newly created texture
    glBindTexture(GL_TEXTURE_2D, renderedTexture);

    // give the image to opengl
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, data);

    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);

    glBindTexture(GL_TEXTURE_2D, 0);
    return renderedTexture;
}
void drawImage(unsigned glTxt, float tx, float ty, float bx, float by, float z) {
    //glEnable(GL_BLEND);
    //glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

    glEnable(GL_TEXTURE_2D);
    glBindTexture(GL_TEXTURE_2D, glTxt);

    glBegin(GL_TRIANGLE_FAN);
        glTexCoord2f(0, 1);
        glVertex3f(tx, ty, z);

        glTexCoord2f(0, 0);
        glVertex3f(tx, by, z);

        glTexCoord2f(1, 0);
        glVertex3f(bx, by, z);

        glTexCoord2f(1, 1);
        glVertex3f(bx, ty, z);
    glEnd();

    glDisable(GL_TEXTURE_2D);
    glDisable(GL_BLEND);
}

    //...
    wglMakeCurrent(it->second->hDC, it->second->hRC);

    //create the texture + load the texture
    unsigned glTxt = createGLTexture((right - left), (bottom - top), &bfr[0]);

    //render the texture to the correct screen positions
    setWidthHeightRender((right - left), (bottom - top));

    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
    glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);

    drawImage(glTxt, 0.0, 0.0, (right - left), (bottom - top), 0.0f);

    //swap the buffers
    SwapBuffers(it->second->hDC);

    //unload the texture
    glDeleteTextures(1, &glTxt);
    //...

A possible reason might be that rows of texture images have to be aligned to 4. May be, you allocated/read/stored too less data for the complete image. (Please, note that OpenGL textures use images from top to bottom. Hence, it would make sense that artifacts appear at the top.) However, these artifacts could be caused by any other out-of-bound access as well. — Scheff's Cat, May 25 '19 at 05:37

ceorron · Accepted Answer · 2019-05-25T12:32:36.577

I found the answer, it turned out to be a problem with my window width and height that I was getting from windows.

I was setting the window size using the width and height that I was also using to get the texture using glTexImage2D.

SetWindowPos(glWindow->hWnd, 0,
             0, 0, glWindow->width, glWindow->height,
             SWP_NOMOVE | SWP_NOZORDER);

However this sets the window size, what I needed to set was the client area size as this is what is received with a call to glTexImage2D. To set the client area size you should instead use:

RECT Rect;
Rect.left =     (long)glWindow->x_pos;                  // Set Left Value To x_pos
Rect.right =    (long)glWindow->x_pos+glWindow->width;      // Set Right Value To x_pos+width
Rect.top =      (long)glWindow->y_pos;                  // Set Top Value To y_pos
Rect.bottom =   (long)glWindow->y_pos+glWindow->height;     // Set Bottom Value To y_pos+height

AdjustWindowRectEx(&Rect, glWindow->dwStyle, FALSE, glWindow->dwExStyle);
SetWindowPos(glWindow->hWnd, 0,
             0, 0, Rect.right-Rect.left, Rect.bottom-Rect.top,
             SWP_NOMOVE | SWP_NOZORDER);

    //...
    //bind the texture for modification
    glBindTexture(GL_TEXTURE_2D, glWindow->renderedTexture);

    //Now correct width and height used here (and else where) matching client area.
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, glWindow->width, glWindow->height, 0, GL_RGB, GL_UNSIGNED_BYTE, 0);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    //...

OpenGL, unusual artifacts on rendered texture, render co-ordinates?

1 Answers1