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<TITLE>ClanLib Game SDK: Using OpenGL, ClanLib API overview</TITLE>
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<h1>Using OpenGL, ClanLib API overview</h1>
<h2>Abstract:</h2>
<p>This document explains how to use OpenGL in ClanLib.</p>
<h3>Why use ClanLib for OpenGL?</h3>
<p>OpenGL is already a crossplatform library - most distroes even include
GLUT, which removes the platform dependant initialization. Why use ClanLib
then?</p>
<p>The answer is that ClanLib provides much more than simply its display
support. You will get access to the 2D functionality, crossplatform sound,
networking and a nice framework for it all.</p>
<h3>Initializing clanGL</h3>
<p>In order to use <a href="http://opengl.org">OpenGL</a> in ClanLib, you
will have to link against clanGL, and initialize it. You do this by calling
the functions in <a href="../Reference/html/CL_SetupGL.html">CL_SetupGL</a>, accordingly to the system
explained in the <a href="getting_started.html">Getting Started</a>
document:</p>
<ul><pre><font face="Arial,Courier New,Courier">#include <ClanLib/application.h>
#include <ClanLib/core.h>
#include <ClanLib/display.h>
#include <ClanLib/gl.h>
class MyApp : public CL_ClanApplication
{
public:
virtual int main(int argc, char **argv)
{
CL_SetupCore::init();
CL_SetupGL::init();
// Select the display target
CL_SetupDisplay::init();
// Select GLX/ WGL attributes (optional)
CL_OpenGL::set_buffer_size(16);
CL_OpenGL::set_depth_size(16);
// Select the video mode
CL_Display::set_videomode(640, 480, 16, false);
while (!CL_Keyboard::get_keycode(CL_KEY_ESCAPE))
{
// Do CL_Display or OpenGL calls here:
CL_Display::clear_display();
glBegin(GL_TRIANGLES);
// ...
glEnd();
// Show the frame:
CL_Display::flip_display();
// Update input and other stuff:
CL_System::keep_alive();
}
CL_SetupGL::deinit();
CL_SetupDisplay::deinit();
CL_SetupCore::deinit();
return 0;
}
} my_app;
</font></pre></ul>
<p>The important thing to note here is, that the OpenGL context is first
created and select when a video mode is set. So do not make calls to OpenGL
before that.</p>
<h3>ClanLib 2D and OpenGL</h3>
<p>You can use the normal 2D gfx operations that ClanLib offers together
with OpenGL. Note that ClanLib uses OpenGL to emulate them, so you cannot
use them between glBegin()/glEnd() calls.</p>
<p>If you are going to do a lot of 2D calls after each other, you should use
the <a href="../Reference/html/CL_OpenGL.html">CL_OpenGL</a>::begin_2d() and
<a href="../Reference/html/CL_OpenGL.html">CL_OpenGL</a>::end_2d() functions. Those will inform
ClanLib that OpenGL won't be touched, and that it can leave OpenGL in a
state suitable for 2D. If you do not call those, ClanLib will save the
current state of OpenGL, and restore it again, between each 2D
operation.</p>
<h3>The CL_Texture class</h3>
<p>ClanLib can help you with loading textures into an OpenGL texture. The
class <a href="../Reference/html/CL_Texture.html">CL_Texture</a> creates a texture handle and uses a
surface provider to load the texture:</p>
<ul><pre><font face="Arial,Courier New,Courier">CL_Texture *texture1 = CL_Texture::load("image", resources);
CL_Texture *texture2 = CL_Texture::create(
new CL_TargaProvider("texture.tga", NULL),
true);
</font></pre></ul>
<p>To use the texture, you will have to bind it. To do that, call
CL_Texture::bind().</p>
<p>If the surface provider contain sub frames, each of those frames will
become a texture. You will have to specify to CL_Texture::bind() which sub
frame you want to use.</p>
<ul><pre><font face="Arial,Courier New,Courier">texture1->bind();
glBegin(GL_QUADS);
glColor3f(1.0f, 1.0f, 1.0f);
glTexCoord2f(0.0f, 0.0f);
glVertex3f(10,10,10);
glTexCoord2f(1.0f, 0.0f);
glVertex3f(20,10,10);
glTexCoord2f(1.0f, 1.0f);
glVertex3f(20,10,20);
glTexCoord2f(0.0f, 1.0f);
glVertex3f(10,10,20);
glEnd();
</font></pre></ul>
<h3>The future</h3>
<p>At the moment, this is all ClanLib will help you with, if you're going to
use OpenGL. For the rest, you will either have to do it yourself, or go
hunting on the 'net for a library that can help you.</p>
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<FONT COLOR="#a0a0a0">Questions or comments, write to the <a href="mailto:clanlib-user.x.dtu.dk">ClanLib mailing list</a>.</FONT>
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