Rotating rectangles

[Vimm]

I need the rectangles that spawn in my game to rotate as they move, so I made an angle variable and put

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love.graphics.rotate(angle)

in my draw function just above the rectangle spawning for loop, then i put

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angle = angle + dt * math.pi/2
angle = angle % (2*math.pi)

in my update function, like the love wiki page on graphics.rotate says to do, and I got a weird result, the rectangles are now spinning as if they're orbiting something of screen, and really fast. Which isn't what I wanted at all.

How do I make it so the rectangles rotate on a center axis, and how do I make them rotate a bit slower.

I've included the .love, even though its just a main.lua right now

[s-ol]

You need to learn how transforms work. rotate rotates around the point (0, 0), if you want to rotate a rectangle art (x,y) around its center you need to do:

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love.graphics.translate(x, y) -- move relative (0,0) to (x,y)
love.graphics.rotate(angle) -- rotate coordinate system around relative (0,0) (absolute (x,y))
love.graphics.rectangle("fill", -w/2, -h/2, w, h) -- draw rectangle centered around relative (0,0)

Remember that order matters und you need to use push and pop for multiple rectangles.

[Vimm]

You need to learn how transforms work. rotate rotates around the point (0, 0), if you want to rotate a rectangle art (x,y) around its center you need to do:

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love.graphics.translate(x, y) -- move relative (0,0) to (x,y)
love.graphics.rotate(angle) -- rotate coordinate system around relative (0,0) (absolute (x,y))
love.graphics.rectangle("fill", -w/2, -h/2, w, h) -- draw rectangle centered around relative (0,0)

Remember that order matters und you need to use push and pop for multiple rectangles.

Oh ok, I read on some forums not to use translate for some reason.

So I did that and it's closer to what I need, but still not quite right, I assume it's because im not "pushing and popping" (lol), since I don't know what that means xD

(edited love file included)

[Sulunia]

Push means the following rotating, transforming and drawing functions will happen on a separate layer until you pop it.
So if you push, translate and rotate for a given rectangle, draw it and then pop, anything you draw after the pop wont rotate.

Did that make any sense? Perhaps someone can explain this a bit better

[davisdude]

If you want to rotate the rectangle about its center do something like this:

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function rotatedRectangle( mode, x, y, w, h, rx, ry, segments, r, ox, oy )
	-- Check to see if you want the rectangle to be rounded or not:
	if not oy and rx then r, ox, oy = rx, ry, segments end
	-- Set defaults for rotation, offset x and y
	r = r or 0
	ox = ox or w / 2
	oy = oy or h / 2
	-- You don't need to indent these; I do for clarity
	love.graphics.push()
		love.graphics.translate( x + ox, y + oy )
		love.graphics.push()
			love.graphics.rotate( -r )
			love.graphics.rectangle( mode, -ox, -oy, w, h, rx, ry, segments )
		love.graphics.pop()
	love.graphics.pop()
end

-- later
rotatedRectangle( 'line', 100, 100, 50, 50, math.pi / 4 )

This could also be achieved using canvases.

[s-ol]

@OP: I can't think of a reason not to use transform. Learn how to use the matrix transforms, it's important graphics stuff.

This could also be achieved using canvases.

You will have to apply the exact sake transformations and waste precious vram on a single-color rectangle, I dont see the point.

[davisdude]

I worded that poorly. I meant to say that you can use this same principle to rotate an entire image with a canvas.

[Ref]

Hay, davidude!
Think you got carried away with the pushing and popping.
Only need one push and one pop.
Best

[darkfrei]

As easy as possible (rotated about the middle):

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function drawRotatedRectangle(mode, x, y, w, h, angle)
	love.graphics.push()
		love.graphics.translate(x, y)
		love.graphics.rotate(angle)
		love.graphics.rectangle(mode, -w/2, -h/2, w, h)
	love.graphics.pop()
end