game works now

.gitignore

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+./art
+.run

app/bounce.rb

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+# A = old position, c = center of ball, v = current moving vector
+def reflection_vector(ax,ay,cx,cy,xv,yv)
+  # Bouncing of resulting point: R
+  rx = ax + xv
+  ry = ay + yv
+  ux = rx - cx
+  uy = ry - cy
+
+  r = (-ux*cx + ux*ax -uy*cy + uy*ay).to_f / ( ux * ux + uy * uy).to_f
+
+  fx = cx + r * ux
+  fy = cy + r * uy
+
+  afx = fx - ax
+  afy = fy - ay
+
+  gx = ax + 2 * afx
+  gy = ay + 2 * afy
+
+  rgx = gx - rx
+  rgy = gy - ry
+
+  return rgx,rgy
+end
+
+
+# x,y further away than r allows?
+def bouncing?(x,y,cx,cy,r)
+  # d(cx,cy,x,y) > r?
+  d = Math.sqrt((x - cx)*(x-cx) + ( y - cy)*( y - cy))
+
+  d > r
+end
+
+# if the speed vector is higher than the radius, we are done (2x radius would be still okay actually)
+def too_fast?(vx,vy,r)
+  d = Math.sqrt(vx*vx+vy*vy)
+
+  d > r
+end

app/main.rb

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+require "app/bounce.rb"
+
+BOUNCE_ACCL = 1.02
+GRAVITY = 0.9
+CX = 636
+CY = 399
+CR = 205
+
+def tick args
+  # INIT
+  # circle
+  cx = CX
+  cy = CY
+  cr = CR
+  # pause
+  args.state.paused = false if args.state.paused.nil?
+  if args.state.ball.nil?
+    args.state.ball = {
+      x: 500,
+      y: 500,
+    }
+    args.state.ball_vector = {
+      x: 0,
+      y: 0
+    }
+  end
+
+  # INPUT
+  if args.inputs.keyboard.key_up.space
+    args.state.paused = !args.state.paused
+  end
+
+  # LOOP
+  if !args.state.paused
+    #ball vector
+    move_x = args.state.ball_vector[:x]
+    move_y = args.state.ball_vector[:y]
+    # apply gravity
+    move_y = move_y - GRAVITY
+    args.state.ball_vector[:x] = move_x
+    args.state.ball_vector[:y] = move_y
+
+    # bounce
+    x = args.state.ball[:x]
+    y = args.state.ball[:y]
+    new_x = x + move_x
+    new_y = y + move_y
+    if bouncing?(new_x,new_y,cx,cy,cr)
+      new_move_x, new_move_y = reflection_vector(x,y,cx,cy,move_x,move_y)
+      args.state.ball_vector[:x] = new_move_x * BOUNCE_ACCL
+      args.state.ball_vector[:y] = new_move_y * BOUNCE_ACCL
+    end
+
+    # move the ball
+    move_x = args.state.ball_vector[:x]
+    move_y = args.state.ball_vector[:y]
+    args.state.ball[:x] = args.state.ball[:x] + move_x
+    args.state.ball[:y] = args.state.ball[:y] + move_y
+  end
+
+  # END?
+  if !args.state.paused
+    if too_fast?(move_x, move_y, cr)
+      #RESET state and pause
+      args.state.ball = {
+        x: 500,
+        y: 500,
+      }
+      args.state.ball_vector = {
+        x: 0,
+        y: 0
+      }
+      args.state.paused = true
+    end
+  end
+
+
+  # RENDER
+  #
+  # BG
+  args.outputs.sprites << {
+    x: 0,
+    y: 0,
+    w: 1280,
+    h: 720,
+    path: 'sprites/BG1.png' }
+
+  if  args.state.paused
+    args.outputs.labels  << [640, 40, "Game is paused. Press <space> to continue", 4, 1]
+  end
+
+  # BALL
+  args.outputs.sprites << {
+    x: args.state.ball[:x]-16,
+    y: args.state.ball[:y]-16,
+    w: 32,
+    h: 32,
+    path: 'sprites/ball.png' }
+end

metadata/game_metadata.txt

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+devid=squishibutz
+devtitle=Squishibutz
+gameid=Bouncing
+gametitle=Sguis Bouncing
+version=0.1
+icon=metadata/bounce_@1.png

run

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+../dragonruby-macos/dragonruby ./