Alright... short story is that stuff like this always happens when I try and do graphics. One thinks I would learn, but apparently I'm a masochist. So...

Nothing really fancy, small project that sets up a window to draw to.

What I am trying to achieve, for personal reasons, is to write my own rasterizer.

So first things first here are some links to the issue that I am encountering:

https://www.dropbox.com/s/fmuk9rycvnnyqqg/HATE.png

https://www.dropbox.com/s/dyqibeo31qc448y/HATE%202.png

https://www.dropbox.com/s/979twrhf1g8dkcx/HATE%203.png

And here is the code:

Creating the view:

wglMakeCurrent(hdc, hglrc);

glClearColor(0.5f, 0.1f, 0.15f, 1.0f);
glClearDepth(1.0f);
glShadeModel(GL_FLAT);

int width = 0;
int height = 0;
_renderTarget->GetSize(&width, &height);

glViewport(0, 0, width, height);

glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(-width/2, width/2, -height/2, height/2, -1.0, 1.0);

glMatrixMode(GL_MODELVIEW);
glLoadIdentity();

Render the fixed function test background

  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

  glPushMatrix();
  glRotatef(_spin, 0.0f, 0.0, 1.0f);
  glColor3f(0.3f, 0.1f, 0.15f);
  glRectf(-150.0f, -150.0f, 150.0f, 150.0f);
  glPopMatrix();

  _rasterizer->Render();

  HDC hdc = GetDC(_renderTarget->GetHandle());
  SwapBuffers(hdc);
  ReleaseDC(_renderTarget->GetHandle(), hdc);

Render my rasterizer

  glBegin(GL_POINTS);
  glPushMatrix();
  int const RenderBufferSize = m_bufferWidth * m_bufferHeight;
  for (int i = 0; i < RenderBufferSize; ++i)
  {
    int x = i % m_bufferWidth;
    int y = i / m_bufferWidth;
    int halfWidth = m_bufferWidth / 2;
    int halfHeight = m_bufferHeight / 2;

    glColor4ubv(m_renderBuffer);
    glVertex2i(x - halfWidth, halfHeight - y);
  }
  glPopMatrix();
  glEnd();

Hopefully that is enough info, if not just ask.

Any help is greatly appreciated.

So what is the issue?

The first image shows the issue: when I draw points on the left half of the screen it seems to decide to skip a few columns. It's an 800x600 window and I'm drawing 800x600 points.

Second and third images show me drawing my rasterizer to a localized region of the window (400x300 points).

--

In:

int x = i % m_bufferWidth;
int y = i / m_bufferWidth;
int halfWidth = m_bufferWidth / 2;
int halfHeight = m_bufferHeight / 2;

Shouldn't it be:

int y = i / m_bufferHeight;

No, as it is an array that I am indexing. As such, the rows are calculated as (i / width).

--

And why are you using prehistorical OpenGL? Or are you stuck with good-for-nothing video card (like I am)?

Because I was referencing openGL books I had on hand.

--

It's just frustrating that I tell the thing to render 800x600 points and it apparently gets lazy halfway through.

Is there a reason you're drawing all those vertices? Wouldn't it be easier to create a texture and render it on a fullscreen quad?

Is there a reason you're drawing all those vertices? Wouldn't it be easier to create a texture and render it on a fullscreen quad?

From what I saw, rendering to a texture was about as equivalent to rendering to the screen. i.e. you just targeted a different framebuffer that was bound to a texture.

Maybe I missed something?

All right, got it fixed. It's been too long since I last touched graphics stuff so I forgot about the whole 0.5 pixel location thing. Which is one of the reasons that I'm doing this... experiment.

And yes, I realize that pushing to a texture and rendering a quad is the better solution but when I looked for how to do this, all I got was this whole binding a frame buffer to a texture and doing the draw calls to that. Ergo, it seemed pointless to go that route.

Thanks.

And yes, I realize that pushing to a texture and rendering a quad is the better solution but when I looked for how to do this, all I got was this whole binding a frame buffer to a texture and doing the draw calls to that. Ergo, it seemed pointless to go that route.

You probably want something like this:

// Initialization
glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, 0);

// Updating
glBindTexture(GL_TEXTURE_2D, texture);
glTexSubImage2D(GL_TEXTURE_2D, 0, GL_RGB, 0, 0, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, pixels);

// Rendering
glBindTexture(GL_TEXTURE_2D, texture);
glBegin(GL_QUADS);
glTexCoord2f(0,1); glVertex2f(-1, -1);
glTexCoord2f(1,1); glVertex2f( 1, -1);
glTexCoord2f(1,0); glVertex2f( 1,  1);
glTexCoord2f(0,0); glVertex2f(-1,  1);
glEnd();

Hopefully got all that correct because I just typed it in there :p And that "pixels" is your "m_renderBuffer".