attraction, slingshot demo

main.lua

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+function love.load()
+ b = love.graphics.newImage("Snow_Ball.png")
+ b_x, b_y = 100, 100
+ b_w, b_h = 36, 36
+
+ v_x, v_y = 0, 0
+ love.graphics.setColor(255,255,255)
+ love.graphics.setBackgroundColor(0,0,0)
+
+ a = 0
+ a_k = 500 
+end
+
+function love.draw()
+ local x, y = love.mouse.getPosition()
+ love.graphics.draw(b, b_x, b_y)
+
+ if love.mouse.isDown(2) then
+ love.graphics.line(x,y,b_x+b_w/2,b_y+b_h/2)
+ end
+ love.graphics.print("k="..a_k .." a="..a, 10, 10)
+end
+
+function love.update(dt)
+ local x, y = love.mouse.getPosition()
+
+ if love.mouse.isDown(1) then
+ b_x = x - b_w / 2
+ b_y = y - b_h / 2
+ return -- quit function?
+ elseif love.mouse.isDown(2) then
+ local t = love.timer.getTime()
+ local dx, dy = x - b_x, y - b_y
+ local d = norm(dx, dy)
+ local d = math.max(d, 10)
+ -- local k = 500
+ -- a = k * (t - t_start) / (d*d)
+ k = 500
+ a = a_k / (d*d)
+ v_x = v_x + dx/d * a
+ v_y = v_y + dy/d * a 
+
+ end
+
+ b_x = b_x + v_x * dt
+ b_y = b_y + v_y * dt
+end
+
+function love.mousepressed(x, y, button, istouch)
+ if button == 1 then
+ x_press = x
+ y_press = y
+ end
+ if button == 2 then
+ t_start = love.timer.getTime()
+ end
+end
+
+function love.mousereleased(x, y, button, istouch)
+ if button == 1 then
+ local k = 5
+ v_x = k * (x_press - x)
+ v_y = k * (y_press - y)
+ end
+end
+
+function love.wheelmoved(x, y)
+ a_k = a_k + 20 * y
+end
+
+function norm(x, y)
+ return math.sqrt(x*x+y*y)
+end