Real time physics body scaling issue in Corona SDK

Question

my goal is to create a platform, from one x,y coordinate, to the touch event, in such a way that sliding your finger around will move and resize the platform in real time. However the problem is, that if there is a ball on said platform, and i then move the platform, The ball will freeze and stop acting like a ball, until the platform is done being manipulated.

Is there a way that I can get the balls to continue to behave as normal even while the platform they are on is being moved?

I have included the code so you can play with it and see what I mean. The best way to see what I am talking about is to click to create a platform, wait for a ball to land on it, and then drag the end of the platform around.

        local physics = require("physics");
physics.start();
physics.setDrawMode("hybrid");
W = display.contentWidth;
H = display.contentHeight;

balls = {};

local function createPlatform(event)
    if (event.phase == "began") then
        if(line) then
            line.parent:remove(line);
        end
        x = (event.x - (W/2 - 80));
        y = (event.y - (H/2));
        line = display.newLine(W/2 - 80, H/2, event.x, event.y)
        line.width = 5;
        physics.addBody(line, "static", {shape = {0, 0, x, y}});
        line.isBullet = true;
    end
    if (event.phase == "moved") then
        x = (event.x - (W/2 - 80));
        y = (event.y - (H/2));
        if (line) then
            line.parent:remove(line);
        end
        line = display.newLine(W/2 - 80, H/2, event.x, event.y)
        line.width = 5;
        physics.addBody(line, "static", {shape = {0, 0, x, y}});
        line.isBullet = true;
    end
    if (event.phase == "ended") then

    end
end

local function spawnBalls(event)

    i = 1;
    local function spawnb(event)
        rand = math.random(1, 4);
            if (rand == 1) then
                balls[i] = display.newCircle(math.random(140, 180), -30, 7.5);
                balls[i]:setFillColor(255,0,0);
                physics.addBody(balls[i], {radius = 7.5})
                balls[i].isBullet = true;
                i = i + 1;
                rand = math.random(1,4)
            elseif (rand == 2) then
                balls[i] = display.newCircle(math.random(140, 180), -30, 7.5);
                balls[i]:setFillColor(0, 255, 0);
                physics.addBody(balls[i], {radius = 7.5})
                balls[i].isBullet = true;
                i = i + 1;
                rand = math.random(1,4)
            elseif (rand == 3) then
                balls[i] = display.newCircle(math.random(140, 180), -30, 7.5);
                balls[i]:setFillColor(0, 0, 255)
                physics.addBody(balls[i], {radius = 7.5})
                balls[i].isBullet = true;
                i = i + 1;
                rand = math.random(1,4)
            elseif (rand == 4) then
                balls[i] = display.newCircle(math.random(140, 180), -30, 7.5);
                balls[i]:setFillColor(255, 255, 0);
                physics.addBody(balls[i], {radius = 7.5})
                balls[i].isBullet = true;
                i = i + 1;
                rand = math.random(1,4)
            end
        end
    timer.performWithDelay(1500, spawnb, -1);
end

spawnBalls();

Runtime:addEventListener("touch", createPlatform)

Iansen Iansen · Accepted Answer · 2012-02-13T16:22:43

I think this happens because you remove the body (line) before Box2D has a chance to calculate new positions/velocities for bodies (when moving your finger, mouse on screen) ... you could try increasing position iterations and frame rate...but this is not really recommended due to performance loss.
I would recommend rotating and scalling the body with out removing it and and adding a new one. You can use .rotation and .xScale/.yScale.

Haven't tried it but this is how I would do it. I'm kind of new to Corona too...so no guarantees.

Real time physics body scaling issue in Corona SDK

1 Answers