[Gambas-devel] Interface of gb.opengl.sge

[Benoît Minisini]

Le 28/03/2013 09:24, Tomek a écrit :
> On 28.03.2013 02:41, Benoît Minisini wrote:
>> Hi Tomek,
>>
>> I took a glance at your code, and I strongly suggest the following
>> changes to the gb.opengl.gse interface before you go further.
>>
>> Why these changes? Mainly because I try to make Gambas components have
>> the most similar interfaces as possible, so that the learning curve is
>> lower.
>>
>> By the way, not that there is a design problem too : the MD2 model
>> loading routine only works if the endianness of the CPU is the same as
>> the endianness of the file. You should ensure that if the endianness is
>> different, you swap the binary data accordingly.
>>
>> Now the old interface :
>>
>> GB_DESC Md2ModelDesc[] =
>> {
>>      GB_DECLARE("Md2Model", sizeof(MD2MODEL)),
>>      GB_NOT_CREATABLE(),
>>      GB_STATIC_METHOD("Load", "Md2Model" , Md2Model_Load, "(Name)s"),
>>      GB_METHOD("SetPosition", NULL, Md2Model_SetPosition, "(X)f(Y)f(Z)f" ),
>>      GB_METHOD("DrawFrame", NULL, Md2Model_DrawFrame,
>> "(Frame_No)i(Texture)i" ),
>>      GB_METHOD("DrawInterFrame", NULL, Md2Model_DrawInterFrame,
>> "(Frame_No)i(InterFrame)f(Texture)i" ),
>>      GB_METHOD("GetFramesNo", "i", Md2Model_GetNoFrames, NULL ),
>>      GB_METHOD("GetFrameName", "s", Md2Model_GetFrameName, "(FrameNumber)i" ),
>>      GB_METHOD("Scale", NULL, Md2Model_Scale,
>> "(Scale_x)f(Scale_y)f(Scale_z)f" ),
>>      GB_METHOD("_free", NULL, Md2Model_free, NULL ),
>>      GB_END_DECLARE
>> };
>>
>> The new one I suggest:
>>
>> GB_DESC Md2ModelDesc[] =
>> {
>>      GB_DECLARE("Md2Model", sizeof(MD2MODEL)),
>>      GB_NOT_CREATABLE(),
>>      GB_STATIC_METHOD("Load", "Md2Model" , Md2Model_Load, "(Name)s"),
>>      // 'SetPosition' renamed to 'Move'
>>      GB_METHOD("Move", NULL, Md2Model_SetPosition, "(X)f(Y)f(Z)f" ),
>>      // Three properties to get/set the one coordinate
>>      GB_PROPERTY("X", "f", Md2Model_X),
>>      GB_PROPERTY("Y", "f", Md2Model_X),
>>      GB_PROPERTY("Z", "f", Md2Model_X),
>>      // A virtual object for accessing frame properties and count
>>      GB_PROPERTY_SELF("Frames", ".Md2Model.Frames"),
>>      GB_METHOD("Scale", NULL, Md2Model_Scale, "(ScaleX)f(ScaleY)f(ScaleZ)f" ),
>>      // Maybe you should add ScaleX, ScaleY and ScaleZ properties too.
>>      GB_METHOD("_free", NULL, Md2Model_free, NULL ),
>>      GB_END_DECLARE
>> };
>>
>> GB_DESC Md2ModelFramesDesc[] =
>> {
>>      GB_DECLARE_VIRTUAL(".Md2Model.Frames"),
>>      // Was Md2Model_GetNoFrames
>>      GB_PROPERTY_READ("Count", "i", Md2Model_Frames_Count)
>>      GB_METHOD("_get", ".Md2Model.Frame", Md2Model_Frames_get, "(Frame)i"),
>>      GB_END_DECLARE
>> }
>>
>> // The _get method of Md2Model_Frames is implemented that way:
>>
>> BEGIN_METHOD(Md2Model_Frames_get, GB_INTEGER frame)
>>
>>      // Store the frame number into the object, it will be used immediately
>>      // by the method called on the virtual .Md2Model.Frame object.
>>      // Maybe check that the frame number is valid now.
>>      // And don't forget to add the 'frame' field into the object
>>      // structure.
>>      THIS->frame = VARG(frame);
>>
>> END_METHOD
>>
>> GB_DESC Md2ModelFrameDesc[] =
>> {
>>      GB_DECLARE_VIRTUAL(".Md2Model.Frame"),
>>      // Was 'Md2Model.DrawFrame'
>>      GB_METHOD("Draw", NULL, Md2Model_Frame_Draw, "(Texture)i"),
>>      // Was 'Md2Model.DrawInterFrame'
>>      GB_METHOD("DrawInterFrame", NULL, Md2Model_Frame_DrawInterFrame,
>> "(InterFrame)f(Texture)i"),
>>      GB_END_DECLARE
>> }
>>
>> Tell me what you think about that and if you have questions!
>>
>> Regards,
>>
> Hi Benoit,
>
> Thanks for your suggestions, I will try to do as much a I can using
> devel-api documentation page. It's the best way to learn I think. When
> I'm stuck, I'll ask for your help, ok?
> Question 1 - How do I check endianess of the CPU from component level?

You must read a well known two or four bytes integer value from the file 
with fread, and see if you get it swapped or not.

If you get it swapped, then you know that all binary values must be swapped.

You can use the magic identifier at the beginning of the file, but 
beware that you must check it byte by byte before reading it as a binary 
data.

Otherwise you may take some files starting with the magic number 
inverted as MD2 model files!

> One more question - what would be the best way to make the class
> creatable - Md2Model_new I suppose, but what should be in that function?
> Can it be empty? Without creatable class I can't make an array of it.

Yes, you must be able to create void models, and manage them in all 
functions.

If a void model must not be used anywhere, you can use the "check hook".

You declare the check hook in the class description structure with:

GB_HOOK_CHECK(my_check_function),

Then 'my_check_function' must be a function taking a pointer to a 
Md2Model object and returning an integer different from zero if that 
object is invalid. (The interpreter will raise the 'Invalid object' error).

Moreover, you must think about implementing boolean operators between 
models if it has some sense (merging two models for example). I have no 
idea, not being an OpenGL expert, but if you want to implement such a 
thing, then a void model must be perfectly valid then.

Regards,

-- 
Benoît Minisini