Attaching multiple shapes to fixture and setting an image

[geocine]

I created a code from this example. https://love2d.org/wiki/Tutorial:Physics

I want to replace the ball object so I created a pig object, I used a program to compute multiple polygon shapes that will be used for my particular object.

Here is my image.

rXc3s.png (17.9 KiB) Viewed 613 times

Here is my code

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	imagePig = love.graphics.newImage("queen_pig.png")
	--let's create the pig
	objects.pig = {}
	objects.pig.body = love.physics.newBody(world, 1024/2, 768/2, "dynamic")
	objects.pig.image = imagePig
	objects.pig.shapes = {
			love.physics.newPolygonShape(9, 46, 8, 44, 8, 38,  14, 36, 11, 46),
			love.physics.newPolygonShape(-33, 14,  -31, 13,  -21, 22,  -33, 17),
			love.physics.newPolygonShape(23, 22,  23, 26,  21, 34,  5, 27,  20, 20),
			love.physics.newPolygonShape(-32, 29,  -36, 24,  -36, 19,  -33, 17,  -21, 22,  -26, 29),
			love.physics.newPolygonShape(28, 17,  20, 20,  28, 12),
			love.physics.newPolygonShape(-17, 37,  -17, 28,  -14, 25,  -3, 27,  -3, 37,  -6, 40,  -12, 40),
			love.physics.newPolygonShape( 8, 38,  7, 33,   14, 36),
			love.physics.newPolygonShape(26, 28,  26, 30,  21, 34,  23, 26),
			love.physics.newPolygonShape(5, 31,  5, 27,  21, 34,  14, 36  ,  7, 33),
			love.physics.newPolygonShape( 21, 41,  19, 41,  14, 36,  21, 34),
			love.physics.newPolygonShape(-17, 25,  -21, 22,  -37, -19,  31, 10,  28, 12,  -14, 25),
			love.physics.newPolygonShape(-29, -29,  -12, -35,  10, -35,  21, -32,  31, 10,  -37, -19 ),
			love.physics.newPolygonShape(32, 34,  32, 36,  21, 34,  26, 30),
			love.physics.newPolygonShape( -36, 8,  -39, 0,  -39, -11  ,  -37, -19,  -21, 22,  -31, 13),
			love.physics.newPolygonShape(34, -21,  37, -12,  36, 1,  31, 10,  21, -32,  28, -28),
			love.physics.newPolygonShape(20, 20,  5, 27,  -3, 27,  -14, 25,  28, 12)
			
		}
	for i=0, table.getn(objects.pig.shapes) do
      objects.pig.fixtures[i] = love.physics.newFixture(objects.pig.body, objects.pig.shapes[i],2)
	  objects.pig.fixtures[i]:setRestitution(0.9) --let the pig to bounce
    end

I tried to store the ploygon shapes into a table/array. Then loop through each shape and add a new fixture for each shape. However I get this error on this line:

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objects.pig.fixtures[i] = love.physics.newFixture(objects.pig.body, objects.pig.shapes[i],2)

Incorrect parameter type: expected userdata

When drawing the ball , the example used this code.

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love.graphics.circle("fill", objects.ball.body:getX(), objects.ball.body:getY(), objects.ball.shape:getRadius())

Now, how do I draw my image with the multiple polygons set? I just don't want it to be a plain circle even though this pig image could actually be a circle.

To make this simple I want to accomplish something like the image below:

lvVRV.png (21.06 KiB) Viewed 613 times

[OmarShehata]

I believe the problem is in your loop here:

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for i=0, table.getn(objects.pig.shapes) do

Tables in Lua start at 1, not 0. So shapes where i is 0 is not defined, and produces an error.

Starting at i=1 should fix this problem.

[geocine]

Thanks Omar,
I updated the code to:

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   objects.pig.fixtures ={}
	for i=1, table.getn(objects.pig.shapes) do
      objects.pig.fixtures[i] = love.physics.newFixture(objects.pig.body, objects.pig.shapes[i],2)
	  objects.pig.fixtures[i]:setRestitution(0.9) --let the ball bounce
    end

Now, how do I see my pig?

When drawing the ball , the example used this code.

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    love.graphics.circle("fill", objects.ball.body:getX(), objects.ball.body:getY(), objects.ball.shape:getRadius())

[Robin]

In love.load(), create a new image, like so:

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pigImage = love.graphics.newImage("pig.png")

And replace that call to love.graphics.circle with

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love.graphics.draw(pigImage, objects.ball.body:getX(), objects.ball.body:getY())

Except you'll probably have another body for it, but yeah.

See documentation for love.graphics.newImage, love.graphics.draw and Image

[Boolsheet]

table.getn is moving into the deprecated area. Use the length operator # instead:

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for i = 1, #objects.pig.shapes do
-- ...
end

First, I suggest you draw the polygons themselves just to make sure they are where you expect them to be.

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for i = 1, #objects.pig.shapes do
	love.graphics.polygon("line", objects.pig.body:getWorldPoints(objects.pig.shapes[i]:getPoints()))
end

And to extend Robin's example:

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love.graphics.draw(imagePig, objects.pig.body:getX(), objects.pig.body:getY(), objects.pig.body:getAngle(), 1, 1, imagePig:getWidth()/2, imagePig:getHeight()/2)

This assumes that the body origin is supposed to be in the center of the image. The last two arguments are the offsets and using the image size divided by two there will make it rotate around the center.

[geocine]

Thanks Robin and Boolsheet.

I tried to draw my polygon and my image using Boolsheet's code. Here is what it looks like. Seems that the polygon is inverted . How do I fix the polygon so that it snaps into the image?

I just want to draw the polygons along with the image for debugging purposes. If I do that though, the body rotates within the center of the image. The image does not rotate with the body.

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for i = 1, #objects.pig.shapes do
   love.graphics.polygon("line", objects.pig.body:getWorldPoints(objects.pig.shapes[i]:getPoints()))
end

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love.graphics.draw(imagePig, objects.pig.body:getX(), objects.pig.body:getY(), objects.pig.body:getAngle(), 1, 1, imagePig:getWidth()/2, imagePig:getHeight()/2)

XHhTj.png (16.87 KiB) Viewed 614 times

[Boolsheet]

This depends on how you got the polygons in the first place. Box2D describes its coordinate system where positive Y goes up. In LÖVE's coordinate system, positive Y goes down. If you use an application that targets Box2D, it will expect the system of Box2D and the shapes appear upside down if you draw them directly in LÖVE.

If you're lucky, you can just multiply all the Y coordinates of the polygon shapes with -1.

[geocine]

Hi Boolsheet, thanks for the reply. I multiplied every Y point to -1 and it worked.

Last, could you help me center the image to the body. Here is my .love file.

[Boolsheet]

Use the offset arguments of love.graphics.draw to get it aligned. Increase the Y offset some more, I guess.

I don't know how you got the polygons. If it's an application it probably also had some kind of offset or assumed the center of the image and the flipping of Y messed that up. Not sure what to recommend beside trial and error.

[geocine]

Thanks Boolsheet. I have updated my exporter template which generates these polygons. Now I have the exact body I needed.

I am now using these polygons:

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love.physics.newPolygonShape(  12.00, -40.50  ,  15.00, -30.50  ,  9.00, -32.50  ,  9.00, -38.50  ,  10.00, -40.50 ),
love.physics.newPolygonShape(  -32.00, -11.50  ,  -20.00, -16.50  ,  -30.00, -7.50  ,  -32.00, -8.50 ),
love.physics.newPolygonShape(  21.00, -14.50  ,  6.00, -21.50  ,  22.00, -28.50  ,  24.00, -20.50  ,  24.00, -16.50 ),
love.physics.newPolygonShape(  -25.00, -23.50  ,  -20.00, -16.50  ,  -32.00, -11.50  ,  -35.00, -13.50  ,  -35.00, -18.50  ,  -31.00, -23.50 ),
love.physics.newPolygonShape(  29.00, -6.50  ,  21.00, -14.50  ,  29.00, -11.50 ),
love.physics.newPolygonShape(  -11.00, -34.50  ,  -5.00, -34.50  ,  -2.00, -31.50  ,  -2.00, -21.50  ,  -13.00, -19.50  ,  -16.00, -22.50  ,  -16.00, -31.50 ),
love.physics.newPolygonShape(  15.00, -30.50  ,  8.00, -27.50  ,  9.00, -32.50 ),
love.physics.newPolygonShape(  24.00, -20.50  ,  22.00, -28.50  ,  27.00, -24.50  ,  27.00, -22.50 ),
love.physics.newPolygonShape(  8.00, -27.50  ,  15.00, -30.50  ,  22.00, -28.50  ,  6.00, -21.50  ,  6.00, -25.50 ),
love.physics.newPolygonShape(  22.00, -28.50  ,  15.00, -30.50  ,  20.00, -35.50  ,  22.00, -35.50 ),
love.physics.newPolygonShape(  -13.00, -19.50  ,  29.00, -6.50  ,  32.00, -4.50  ,  -36.00, 24.50  ,  -20.00, -16.50  ,  -16.00, -19.50 ),
love.physics.newPolygonShape(  -36.00, 24.50  ,  32.00, -4.50  ,  22.00, 37.50  ,  11.00, 40.50  ,  -11.00, 40.50  ,  -28.00, 34.50 ),
love.physics.newPolygonShape(  27.00, -24.50  ,  22.00, -28.50  ,  33.00, -30.50  ,  33.00, -28.50 ),
love.physics.newPolygonShape(  -30.00, -7.50  ,  -20.00, -16.50  ,  -36.00, 24.50  ,  -38.00, 16.50  ,  -38.00, 5.50  ,  -35.00, -2.50 ),
love.physics.newPolygonShape(  29.00, 33.50  ,  22.00, 37.50  ,  32.00, -4.50  ,  37.00, 4.50  ,  38.00, 17.50  ,  35.00, 26.50 ),
love.physics.newPolygonShape(  29.00, -6.50  ,  -13.00, -19.50  ,  -2.00, -21.50  ,  6.00, -21.50  ,  21.00, -14.50 )

And here is how it looks like. Neat.

4ut5W.png (25.33 KiB) Viewed 616 times

Thanks Omar for directing me to codeandweb. Thanks Boolsheet for helping me throughout. I added Karma to both of you.