Better ball velocity in `Ball.lua` class

In pong-5/Ball,lua, the ball velocity along the x-axis and y-axis is not so good compared to pong-4. The ball will either has -100 or 100 velocity along y-axis but will have a random velocity from -50 to 50 along x-axis. As a result, the ball movement is unnatural and does not look like random (we have longer x distance and less y distance. It will be more natural if the x-axis velocity is a fixed big number and y-axis velocity is a random relatively small number). This issue affects all programs with the Ball.lua class. Namely, from pong-5 to pong-12. The issue will be more obvious with the interaction with paddles since the ball x-axis velocity can be captured as drastically being faster or slower after colliding with the paddle (again, the reason is that we have a long x distance).

function Ball:reset()
    self.x = VIRTUAL_WIDTH / 2 - 2
    self.y = VIRTUAL_HEIGHT / 2 - 2
    self.dy = math.random(2) == 1 and -100 or 100
    self.dx = math.random(-50, 50)
end

However, in pong-4/main.lua, it will look like the ball is having a natural and random movement.

function love.keypressed(key)
    -- keys can be accessed by string name
    if key == 'escape' then
        -- function LÖVE gives us to terminate application
        love.event.quit()
    -- if we press enter during the start state of the game, we'll go into play mode
    -- during play mode, the ball will move in a random direction
    elseif key == 'enter' or key == 'return' then
        if gameState == 'start' then
            gameState = 'play'
        else
            gameState = 'start'

            -- start ball's position in the middle of the screen
            ballX = VIRTUAL_WIDTH / 2 - 2
            ballY = VIRTUAL_HEIGHT / 2 - 2

            -- given ball's x and y velocity a random starting value
            -- the and/or pattern here is Lua's way of accomplishing a ternary operation
            -- in other programming languages like C
            ballDX = math.random(2) == 1 and 100 or -100
            ballDY = math.random(-50, 50) * 1.5
        end
    end
end

In summary, the dx and dy velocity of ball in all Ball.lua class should be swapped.

games50 / pong

Better ball velocity in `Ball.lua` class #80