[GEM-dev] Lua again: now with luaglut/luagl

[Frank Barknecht]

Hi,

as I still haven't managed to build LuaGL, I now tested luaglut (0.5)
with Gem, downloaded from here:
http://lua-users.org/files/wiki_insecure/users/VarolKaptan/

This wins over LuaGL in the makeability contest with a README and a
working Makefile, but lacks a bit in documentation. Anyway I still
managed to "port" IOhannes' example posted some time ago from LuaGL to
luaglut easily, and even extend it. 

It's attached and the Pd example also compares rendering many lines
with luagl over rendering them with Gem and double gemheads. Lua wins
by an amazing margin on my machine: Lua is twice as fast as Pd when
rendering 1000 lines here. I guess I'll be using luaglut in Pd quite a
bit from now on, that's too much of a speedup to ignore for the tiny
effort required. ;) 

But one thing, which maybe only Claude can answer, makes me wonder,
probably because I don't yet understand how the combination Lua/Gem/Pd
works in general.

In the Lua file (attached), I have a  method "render()" to do the
rendering. This method is called whenever the object receives a
"gem_state" in its 1st inlet. This looks a bit like black magic to me:
How gets the stuff that M:render() renders with GL-commands finally
get attached to the gem-state and transferred into the Gem-window? 

    function M:in_1(sel, atoms)
        if sel == "gem_state" then
           M:render(self)
        end
    end
    
    function M:render(myself)
        -- Why can't I use "self" directly here??????
        -- "self" seems to be a different table inside M:render(). Why?
        -- myself is not equal to self here
        max = math.max(myself.max, 1)
        glBegin(GL_LINES)
        for i=1,max do
            glColor3d(math.random(), math.random(), 0)
            glVertex2d(0, 0)
            glVertex2d(math.random(-400,400)/100, math.random(-400,400)/100)
        end
        glEnd()
    end

And the second black magic bullet that hit me: Normally all methods of
a Pd class written in Lua get the same "self" passed. But M:render()
seems to be different here: If I try to access the self.max value
directly inside M:render(), it is "nil". Printing "self" in various
places also gives different table-pointers, so the "self" in
M:render() and the "self" in the other methods are different tables. I
worked around this by passing the Pd class "self" as "myself", but for
one this is awkward, and more importantly: I just don't get what makes
M:render() special? 

Anyone with good explanations?

Ciao
-- 
 Frank Barknecht                                     _ ______footils.org__
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require 'luagl'

local M = pd.Class:new():register("pdluagl")

function M:initialize(name, atoms)
    self.inlets = 2
    self.max = 1
    pd.post(tostring(self))
    return true
end

function M:in_1(sel, atoms)
    if sel == "gem_state" then
       M:render(self)
    end
end

function M:in_2_float(f)
    self.max = math.abs(f)
    pd.post(self.max)
end

function M:render(myself)
    -- Why can't I use "self" directly here??????
    -- "self" seems to be a different table inside M:render(). Why?
    max = math.max(myself.max, 1)
    glBegin(GL_LINES)
    for i=1,max do
        glColor3d(math.random(), math.random(), 0)
        glVertex2d(0, 0)
        glVertex2d(math.random(-400,400)/100, math.random(-400,400)/100)
    end
    glEnd()
end