On Sat, 2009-07-18 at 19:09 -0400, Dmitri Toubelis wrote: > Thank Robert, this is very nice explanation. I almost figured it out on my > own but with your help it is all clear now. Another question though, how it > all works with materials? Do I just set source material and use vertex > buffer API to draw?
Yep, you should be able to simply set a source material and call cogl_vertex_buffer_draw (). The state is flushed to OpenGL in a number of steps, but when flushing the material state the layers of the material will setup the OpenGL texture combine mode and determine which texture name is bound to each unit; the blend equations of the material will be converted to OpenGL blending state and the material color will usually translate to a glColor call. Then each of the vertex buffer attributes that are currently enabled will internally result in binding a VBO and corresponding call to glVertexPointer, glColorPointer etc. regards, - Robert P.S. I'm replying from a different address since realized my original reply didn't reach the clutter mainlinglist, so anyone else interested in an overview of the cogl vertex buffer API please see below... > > Regards, > Dmitri > > > -----Original Message----- > From: Robert Bragg [mailto:[email protected]] > Sent: July 18, 2009 6:09 PM > To: Dmitri Toubelis > Cc: [email protected] > Subject: Re: [clutter] Using COGL for 3D drawing > > On Fri, 2009-07-17 at 09:15 -0400, Dmitri Toubelis wrote: > > Hi, > > > > I need to create few 3D objects in clutter and I would like to use > > OpenGL for this. So, what is officially recommended approach for this? > > The officially recommended approach is to use the Cogl vertex buffer API for > this. Although there is some limited Cogl API to allow you to break out into > raw GL in exceptional circumstances, I would discourage this. > If Cogl doesn't already support what you need, I'd much rather discuss > improving Cogl. > > > My thinking was to get absolute coordinates of the actor and then use > > vertex buffer API to draw. Is it right thing to do? Could anyone share > > some code samples? > > If you use the cogl vertex buffer API then you can just create an actor > subclass and use cogl_vertex_buffer_draw () in your paint function. You > shouldn't need to muck about getting the absolute coordinates of any actor > since the geometry will be transformed by the actors model view matrix. This > API is also integrated with the CoglMaterial API. > > Essentially you can use this api something like this: > > typedef struct { > float x, y, z; > float u, v; > uint8_t r, g, b, a; > } MyVertex; > > MyVertex my_vertices[100] = { > ... > }; > > vbo = cogl_vertex_buffer_new (100); /* declares the number of vertices in > your VBO */ > > /* Add X,Y,Z vertex attributes: */ > cogl_vertex_buffer_add ( > vbo, /* handle of vertex buffer object */ > "gl_Vertex", /* name of attribute */ > 3, /* number of components (3 for X, Y and Z) */ > COGL_ATTRIBUTE_TYPE_FLOAT, /* attribute data type */ > FALSE, /* should integer types be normalized [0,1]?: no */ > sizeof (MyVertex), /* stride between vertices */ > &my_vertices[0].x); /* pointer to first vertex attribute */ > > /* Add u,v texture coordinate attributes: */ cogl_vertex_buffer_add (vbo, > "gl_MultiTexCoord0", 2, COGL_ATTRIBUTE_TYPE_FLOAT, FALSE, sizeof (MyVertex), > &my_vertices[0].u); > > /* Add RGBA color attributes : */ > cogl_vertex_buffer_add (vbo, "gl_Color", 4, > COGL_ATTRIBUTE_TYPE_UNSIGNED_BYTE, TRUE, sizeof (MyVertex), > &my_vertices[0].r); > > NOTE: For the unsigned byte color attribute we want the values 0-255 to be > normalized to the range [0,1] > > NOTE: The names "gl_Vertex", "gl_MultiTexCoord0" and "gl_Color" aren't > arbitrary, they correspond to builtin glsl names. Even if you aren't using > glsl you must use the builtin glsl name if one exists, otherwise you are > free to create custom attributes with any name you like. > > You can add multiple "gl_Vertex" attributes - assuming only one is enabled > at draw time. To differentiate them the names can have a detail, such as > "gl_Vertex::active" or "gl_Color::enabled". > > /* Now upload all data from your client side arrays to GPU buffers... > * > * note: at this point if your xyz, texture and color attributes were > * allocated on the heap you could free them if you like here. > * note: calling cogl_vertex_buffer_submit is optional, but if you don't > * explicitly call it then your client side arrays must remain valid > * until you draw e.g. using cogl_vertex_buffer_draw (). > */ > cogl_vertex_buffer_submit (); > > Ideally you would only do the above construction work once and you wouldn't > need to modify your vertex buffer per-frame. > > In your paint function you can then do: > > cogl_vertex_buffer_draw (vbo, COGL_VERTICES_MODE_TRIANGLE_STRIP, 0, 100); > > > If you want to morph your geometry, then you can do that by re-adding the > attributes that change over time. > > Note: if you are morphing geometry then you should avoid uploading more data > than necessary per-frame. To help here it may be best to avoid using > interleaved attributes - as my example above does - (i.e. the vertex buffer > data above is arranged as X,Y,X,U,V,R,G,B,A) For morphing geometry create > separate arrays for each attribute and pass 0 for the stride argument. Then > in your paint function you would do: > > /* apply your morphing.. */ > my_update_vertex_positions(); > /* Re-add just the attributes that have changed... */ cogl_vertex_buffer_add > (vbo, "gl_Vertex",,,0, &my_vertices[0]); > /* note the cogl_vertex_buffer_submit can be skipped since it's > * implied when you call cogl_vertex_buffer_draw() */ > cogl_vertex_buffer_draw (vbo, ...); > > anyhow, that's quite a lot to dump in an email. More details about this API > are available here: > http://www.clutter-project.org/docs/cogl/0.9/cogl-Vertex-Buffers.html > > I hope that helps, > kind regards, > > - Robert > -- Robert Bragg, Intel Open Source Technology Center -- To unsubscribe send a mail to [email protected]
