You're not supposed to use any functions like Plot, Line, etc. but use the pointer to the screen buffer to write the desired pixels directly. As a template for the first assignment, you could start with the Game::Tick function mentioned in the text that draws a vertical line:
void Game::Tick( float a_DT )
Pixel* address = m_Screen->GetBuffer() + 100;
for ( int i = 0; i < 255; i++ ) address[i * 640] = i;
This draws a vertical line from (100, 0) to (100, 255) by directly setting values into the buffer. You should modify this to complete the first assignment. Try getting it to draw a diagonal line first, then when that's working put in the dotted-ness. I'll just give a hint: the difference between drawing a vertical line, a diagonal line, or a dotted diagonal line is just changing one number in this code.
Ah, thanks for that. I really need to learn to read because as you've shown, it was all in the tutorial \\^_\\^
Anyways, I got quite far, though I am still having some problems:
Pixel* address = m_Screen->GetBuffer();
for ( int i = 0; i < 400; i++ ) address[i * (640 + 1)] = 0xffffff;
That works for the diagonal line, though for the dotted line when I replace the 1 with 2, it is in fact dotted but not at the right height.
What did I do wrong, is the code above maybe not the code I am supposed to use?