How to draw jagged pixellated line in OpenGL - opengl

Question

I am able to draw a line using OpenGL, which produces the following result:
However, this line looks smooth and out-of-place compared to the pixellated style of my game. I would prefer a result that looks more like this:
Can someone please give me some tips on how I can get OpenGL to draw a pixellated line like this?
Here is my renderLine() method (using immediate mode, I'm afraid):
public static void renderLine(float x1, float y1, float x2, float y2,
float thickness, float[] colour) {
// Store model matrix to prevent contamination
glPushMatrix();
// Set colour and thickness
glColor4f(colour[0], colour[1], colour[2], colour[3]);
glLineWidth(thickness);
// Draw line
glBegin(GL_LINES);
{
glVertex2f(x1, y1);
glVertex2f(x2, y2);
}
glEnd();
// Restore previous state
glColor4f(1, 1, 1, 1);
glLineWidth(1.0f);
glPopMatrix();
}

Answer 1

There's really nothing built-in in OpenGL to draw such lines.
You could draw a tight quad containing the pixels in the line and use a fragment shader that evaluates which pixels are to be left in and which are to left out.
However, considering that you want the look of all your game to be pixellated, the best solution is to render to a smaller texture and then blit it to the screen with x4 (or whatever factor) nearest neighbor interpolation. Then drawing such line reduces to just a regular GL_LINE without GL_LINE_SMOOTHing.