Perspective projection and camera lookat functions for love2d

matrix_utility.lua

--[[
	matrix utility functions for love2d

	expects vec3 from https://github.com/1bardesign/batteries
]]

return {
	calculate_perspective = function(screen, fov, near, far, into)
		--everything we need
		local aspect = screen[1] / screen[2];
		local f = 1.0 / math.tan(fov / 2.0);
		local xpr = f / aspect;
		local ypr = f;
		local fmn = (far - near);
		local zpr = (far + near) / fmn;
		local zhpr = (2.0 * far * near) / fmn;
		
		--garbage generation
		into = into or {}

		--zero out
		for i = 1, 16 do
			into[i] = 0
		end
		--fill required elements
		--(row major, opposite of in glsl)
		into[1] = xpr
		into[6] = ypr
		into[11] = zpr
		into[12] = zhpr
		into[15] = -1

		return into
	end,
	calculate_camera = function(from, to, natural_up)
		local forward = from:vsub(to):normalisei()
		local right = natural_up:cross(forward):normalisei()
		local up = forward:cross(right):normalisei()
		local d_r = -from:dot(right)
		local d_u = -from:dot(up)
		local d_f = -from:dot(forward)
		return {
			right.x,   right.y,   right.z,   d_r,
			up.x,      up.y,      up.z,      d_u,
			forward.x, forward.y, forward.z, d_f,
			0.0,       0.0,       0.0,       1.0,
		}
	end,
}