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Crates: A Physics Experiment

edited November 2012 in Code Sharing Posts: 5

Well, good evening! There was another topic someone posted a while back which had a very simple example of a box, a ball and a floor. I played with it a bit (longer than I care to admit) and created some code that I think may help others to understand the physics of Codea and using sprites.

Also, I can't help but think there are some code-saving steps I'm missing.

Enjoy, and feel free to offer any feedback!

--# Main -- Crates function setup() saveProjectInfo("Description", "An Experiment in Physics") supportedOrientations(LANDSCAPE_RIGHT) displayMode(FULLSCREEN) angle = 0 spin = 0 strokeWidth(5) stroke(116, 62, 39, 255) Objects:init() --This command establishes all the important information we need about our objects. touches = {} end function drawPoly(body) --This is an invaluable (if not complicated-looking) function from the Physics Lab --example that draws the lines of a polygon on the screen. Renamed for simplicity. pushMatrix() translate(body.x, body.y) rotate(body.angle) if body.shapeType == POLYGON then local points = body.points local a, b for j = 1,#points do a = points[j] b = points[(j % #points)+1] line(a.x, a.y, b.x, b.y) end end popMatrix() end function draw() background(40, 40, 50) physics.gravity(Gravity) --This uses the device orientation as Gravity input. This must be done in the draw() --function so that the orientation is re-assessed every frame. Objects:text() --Because we draw the text first, it will appear BEHIND out background image. sprite("Cargo Bot:Opening Crates",WIDTH/2, 296,WIDTH,296*2) --This doesn't serve any practical purpose aside from drawing a pretty background. drawPoly(walls) --This command draws the lines of a polygon, in this case, the walls. drawPoly(crate) drawPoly(crate2) drawPoly(crate3) drawPoly(gold) --These command draw the lines of the crates. Comment these out if you only --want to see the sprites Objects:draw() --This draws the sprites at the exact location of the polygons! Neat, huh? if CurrentTouch.state == BEGAN or CurrentTouch.state == MOVING then if CurrentTouch.x < WIDTH/2 then spin = 500 gold:applyTorque(spin) end if CurrentTouch.x > WIDTH/2 then spin = -500 gold:applyTorque(spin) end end --This bit of nonsense makes the gold crate spin in the direction of the touch. end --# Objects Objects = class() function Objects:init() --This command establishes all the important information we need about our objects. walls = physics.body(POLYGON, vec2(1,0), vec2(WIDTH,0), vec2(WIDTH,HEIGHT), vec2(0,HEIGHT), vec2(0,1), vec2(20,21), vec2(20,HEIGHT-20), vec2(WIDTH-20,HEIGHT-20), vec2(WIDTH-20, 20), vec2(21,20)) --All these positions might look daunting, but dont worry: These are just --the points of the walls around our experiment. walls.type = STATIC --"STATIC" means "STATIONARY";They don't get to bounce around like our crate. --All of the following is information used to create our crate. Remember, this only --creates the "idea" of the crate. In order to see it on the screen, we need to either --make Codea draw the lines, or draw a sprite at the exact location of the "idea". --Sorry if that sounds a bit philosophical ;) crate = physics.body(POLYGON, vec2(0,0), vec2(100,0), vec2(100,100), vec2(0,100)) --This creates the shape of the crate. (0,0) refers to the position of the shape, --not a position on the screen crate.type = DYNAMIC --This means the shape can move around, unlike our walls crate.x = WIDTH*.25 crate.y = HEIGHT/2 --The position on the screen. If this is done in draw(), the box will not be able --to move since you're telling Codea where to put it every frame crate.restitution = .6 --How much the crate bounces... Try playing with numbers between 0 and 2. crate.sleepingAllowed = false --This command prevents objects from sleeping AKA locking in place once stopped crate.angle = 40 --The angle the shape STARTS at. Again, if this is located in draw(), then you're --telling Codea what the angle MUST be instead of letting it change. crate2 = physics.body(POLYGON, vec2(0,0), vec2(100,0), vec2(100,100), vec2(0,100)) --This creates a second crate with slightly different values crate2.type = DYNAMIC crate2.x = WIDTH*.5 crate2.y = HEIGHT/2 crate2.restitution = .7 crate2.sleepingAllowed = false crate2.angle = 80 crate3 = physics.body(POLYGON, vec2(0,0), vec2(100,0), vec2(100,100), vec2(0,100)) crate3.type = DYNAMIC crate3.x = WIDTH*.75 crate3.y = HEIGHT/2 crate3.restitution = .8 crate3.sleepingAllowed = false crate3.angle = 15 gold = physics.body(POLYGON, vec2(0,0), vec2(100,0), vec2(100,100), vec2(0,100)) gold.type = DYNAMIC gold.x = WIDTH*.5 gold.y = HEIGHT/4 gold.restitution = .5 gold.sleepingAllowed = false end function Objects:draw() pushMatrix() --The rotating of the crate image must be done in a "matrix", otherwise the --rotation command will turn everything on the screen! translate(crate.x, crate.y) --"translate" reorients the position of (0,0). In this case, the position of the --crate is now (0,0), no matter where on the screen it appears! rotate(crate.angle) --So long as the sprite and the polygon rotate at exactly the same angle, they --will overlap exactly. sprite("Cargo Bot:Title Large Crate 1", 50,50, 100, 100) --Since (0,0) was reset to the polygon's exact position, we need to make sure that --the sprite corresponds to the "new" (0,0) popMatrix() pushMatrix() --This will draw a sprite for our second crate translate(crate2.x, crate2.y) rotate(crate2.angle) sprite("Cargo Bot:Title Large Crate 2", 50,50, 100, 100) popMatrix() pushMatrix() translate(crate3.x, crate3.y) rotate(crate3.angle) sprite("Cargo Bot:Title Large Crate 3", 50,50, 100, 100) popMatrix() pushMatrix() translate(gold.x, gold.y) rotate(gold.angle) sprite("Cargo Bot:Crate Yellow 2", 50,50, 100, 100) popMatrix() end function Objects:text() pushMatrix() angle = angle + .5 if angle > 360 then angle = 0 end translate(WIDTH/2,HEIGHT/2) rotate(angle) fontSize(70) font("HoeflerText-Black") fill(116, 62, 39, 255) text("Bounce The Crates!",0,0) popMatrix() end


  • Thanks! many things got more clear now, great boost for a starter.

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