The beauty of using matricies to apply transformations to objects

Niicodemus · May 2013

I took a day off to go back and write up all I had learned while working with matrices in Gideros to apply transformations such as position, rotation, scale, reflection and skew to sprites. @bowerandy, @ar2rsawseen and I had a discussion about it in another thread, but I thought I'd throw up a full explanation of how to use Matrices in this way with Gideros.

http://blog.lotech.org/2013/05/the-beauty-of-using-matricies-to-apply.html

The code is available in my github at

https://github.com/nshafer/Matrix

@ar2rsawseen integrated my changes into GiderosCodingEasy already, so there are a couple places you can get it from.

This was the foundation of the AnchorSprite class I wrote, and I'll be writing about how that works soon, too.

Thanks,
Nathan Shafer

SinisterSoft · May 2013

I really liked your tutorial, it will be a really good reference too. Can't wait for the AnchorSprite class article.

A second tutorial/implementation about 4x4 matrices would be great though.

ar2rsawseen · May 2013

Awesome post

and would love to see real world uses.

I was having an idea of writing something similar about vectors, because there are lots of questions poping up on forum, especially for box2d usage, like how to rotate to specific direction/vector, how to get distance between points, etc.

It seems these are kind of the topics, that some developers missed.

Niicodemus · May 2013

Hmm, you know, I did write a Vector2 class that I've been using, that has all overloaded operators for math operation and a built-in distanceTo method. I could release that, too.

OZApps · May 2013

I think that with the OpenGL2.0 release Gideros should have inbuilt 2D and 3D vector support, it would be quite strange if we still had to rely on an external library.

Niicodemus · May 2013

@SinisterSoft, I've expanded my original post a bit with 3D transform matrices. The basics are all the same, though, so the actual implementation will be up to the reader. I have never done any 3D programming, so I don't have anything to go on there.

OZApps · May 2013

@Niicodemus, appreciate your work on the library, there are some things that should be native to Gideros making it easier to work with, like
* JSON
* Tween
* Vectors
rather than have them as external libraries. I have a C++ library for vectors that can be used as plugins which make it faster than Lua code but again it should be native then it would be worth.

ar2rsawseen · May 2013

@OZApps plugins and native is basically the same. If you can share the lib, I can try to wrap it in Gideros, when I'll have time

I've also been experimenting on native tween lib, but did not notice massive improvements for now (probably due to my poor implementation, not a C coder yet

).

OZApps · May 2013

@ar2rsawseen, one good starting point is the Google hosted project for LuaVec http://code.google.com/p/lua-vec/ and the specific Vector library source can be found at http://code.google.com/p/lua-vec/source/browse/trunk/src/lgcveclib.c

ar2rsawseen · May 2013

@OZApps are you kidding me?
It already have all the lua binding. All that is left to do is add gideros headers and wrap in Gideros plugin init methods:

//adding header in the beginning of file
#include "gideros.h"
 
//wrapping plugin in the end of the file
static void g_initializePlugin(lua_State *L)
{
        //get global package object
        lua_getglobal(L, "package");
        lua_getfield(L, -1, "preload");
 
        //put our plugin name inside with a callback to
        //registering C functions
        lua_pushcfunction(L, luaopen_gcvec);
        lua_setfield(L, -2, "Vec");
 
        lua_pop(L, 2);
}
 
static void g_deinitializePlugin(lua_State *L)
{
 
}
 
//register our plugin with Gideros lib
REGISTER_PLUGIN("Vec", "1.0")

And I think that should do it. For Android you will need a .mk file, for IOS I think it could be simply added to the Xcode project. Haven't dealt with desktop plugins yet.

I will test it later, when I'll have more time

OZApps · May 2013

yes, my point was that it can be created into a plug-in without an issue, but it should be available with Gideros, not as a plug-in but part of the API.

Scouser · May 2013

@OZApps: I would have to agree with internal native implementation

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