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lualove2d

What do the coordinates mean in love.graphics.polygon

I don't know which numbers do what in the coordinates example here. I imagine they mean things like place the top left corner at this position and the bottom right corner at this position, but I don't know which number corresponds to which position.

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I've been trying to fool around with the numbers to get a small green rectangle but keep getting weird results like the following, and don't know which numbers need to be what is order to make the rectangle symmetrical and at the bottom

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This is what the rectangle should look like

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The height of the rectangle is 50, the height of the screen is 1000, and the width of the screen is 1700.

Here's my draw function

function love.draw()
  love.graphics.setColor(0.28, 0.63, 0.05) -- set the drawing color to green for the ground
  love.graphics.polygon("fill", objects.ground.body:getWorldPoints(objects.ground.shape:getPoints())) -- draw a "filled in" polygon using the ground's coordinates
    --  These are the grounds coordinates.      -11650  950 13350   950 13350   1000    -11650  1000

  love.graphics.setColor(0.76, 0.18, 0.05) --set the drawing color to red for the ball
  love.graphics.circle("fill", objects.ball.body:getX(), objects.ball.body:getY(), objects.ball.shape:getRadius())

  love.graphics.setColor(0.20, 0.20, 0.20) -- set the drawing color to grey for the blocks
  love.graphics.polygon("fill", objects.block1.body:getWorldPoints(objects.block1.shape:getPoints()))
  love.graphics.polygon("fill", objects.block2.body:getWorldPoints(objects.block2.shape:getPoints()))
  print(objects.block1.body:getWorldPoints(objects.block1.shape:getPoints()))
end
Solution

  • As described at https://love2d.org/wiki/love.graphics, Löve's coordinate system has (0, 0) at the upper left corner of the screen. X values increase to the right, Y values increase down.

    The polygon function expects the drawing mode as it's first parameter, and the the remaining (variable) parameters are the coordinates of the vertices of the polygon you wish to draw. Since you want to draw a rectangle you need four vertices/eight numbers. You do not have to list the upper left corner of the rectangle first, but that's probably the easiest thing to do.

    So in your case, you want something like:

    love.graphics.polygon('fill', 0, 950, 0, 1000, 1700, 1000, 1700, 950)

    I've not worked with the physics system, so I'm not quite sure how it's coordinate system relates to "screen" coordinates. The values you show in the comment in your code listing seem like they should give a rectangle (although x = -11650 wouldn't be on screen). You might try experimenting without the physics system first.

    Also, since the physics system in Löve is just a binding to Box2D, you might want to read its documentation (http://box2d.org/about/). Not really sure what you're trying to do with feeding shape:getPoints into body:getWorldPoints.