How to draw rectangles, circles

Questions
#1

Is there any way to draw simple shapes like rectangles, circles and give them colors for testing purposes?

#2

Using draw_line message you can draw anything you want. For example:

local function draw_circle (position, radius, segment_count)
	local step = math.rad(360) / segment_count
	local point_a = vmath.vector3(position.x + radius, position.y, 0)
	local color = vmath.vector4(1, 0, 1, 1)
	for i = 1, segment_count do
		local angle = i * step
		local point_b = vmath.vector3(position.x + radius * math.cos(angle), position.y + radius * math.sin(angle), 0)
		msg.post("@render:", "draw_line", { start_point = point_a, end_point = point_b, color = color } )
		point_a = point_b
	end
end -- draw_circle

For debugging purposes, of course.

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#3

Could you have the shapes as sprites and tint them? @Pkeod don’t you have a repo with basic shapes?

#4

I never published that one but I could put it up sometime this month. It uses buffers to draw shapes on.

3 Likes
#5

Ah, I thought it was an atlas with png shapes.

#6

Thanks for the reply.
In other engines where they already have the feature to draw basic shapes, is this how it’s done there also? just loop a line around some points?

#7

With a proper drawing API there’s probably functions such as:

draw.line(from, to)
draw.rectangle(bounds)
draw.circle(pos, radius)

And so on…

#8

Defold needs a primitive drawing extension imo. (If extensions even have that kind of power)

#9

Yep, they do. The buffer api allows an extension to modify a texture.

#10

I sadly do not speak C/C++ well, nor do I know anything about openGL (which im assuming is the underlying library?)

In any case, im sure somebody will come along and work on something like this. I do consider it fairly important

edit: or am i understanding that pkeod has already done something?

#11

Yes, maybe :slight_smile: Poll for a next LIb/NE

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#12

I miss an ability to draw primitives as meshes/polygons. So I can easily manipulate vertices from Lua and transform the shapes like I do in Corona.

5 Likes
#13

Since this discussion is the first google result for drawing shapes, I wanted to link to AGulev’s drawpixels extension here: https://github.com/AGulev/drawpixels. This has examples for drawing rectangles and circles.

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