Dumb but accurate triangle rasteriser with top-left fill

Triangle.cpp

void RasteriseTriangle3(char* buffer, int width, int height, float2 v0, float2 v1, float2 v2)
{
	// Sort vertices along the y-axis, lowest first
	if (v1.y < v0.y)
		std::swap(v0, v1);
	if (v2.y < v1.y)
		std::swap(v1, v2);
	if (v1.y < v0.y)
		std::swap(v0, v1);

	// Setup top half gradients
	float dxdy1 = (v1.x - v0.x) / (v1.y - v0.y);
	float dxdy2 = (v2.x - v0.x) / (v2.y - v0.y);

	// Round-up the start/end y for top-left fill convention
	int y = (int)ceil(v0.y);
	int nb_y_steps = (int)ceil(v1.y) - y;
	buffer += (int)y * width;

	// Start x with a pre-step based on how much rounding was performed for fill convention
	float x1 = v0.x + dxdy1 * (y - v0.y);
	float x2 = v0.x + dxdy2 * (y - v0.y);

	// Draw the two halves of the triangle
	for (int i = 0; i < 2; i++)
	{
		for (int y_step = 0; y_step < nb_y_steps; y_step++)
		{
			// Determine which edge is left/right
			float l = x1, r = x2;
			if (r < l)
				std::swap(l, r);

			// Round-up the start/end x for top-left fill convention
			int left = (int)ceil(l);
			int right = (int)ceil(r);

			memset(buffer + left, 255, right - left);

			// Increment for next line
			buffer += width;
			x1 += dxdy1;
			x2 += dxdy2;
		}

		// Setup gradient, y-steps and x with pre-step for the final edge
		dxdy1 = (v2.x - v1.x) / (v2.y - v1.y);
		y = (int)ceil(v1.y);
		nb_y_steps = (int)ceil(v2.y) - y;
		x1 = v1.x + dxdy1 * (y - v1.y);
	}
}