GL

Low-level graphics library.

Use this class to manipulate active transformation matrices, issue rendering commands similar to OpenGL's immediate mode and do other low-level graphics tasks. Note that in almost all cases using Graphics.DrawMesh is more efficient than using immediate mode drawing.

GL immediate drawing functions use whatever is the "current material" set up right now. The material controls how the rendering is done (blending, textures, etc.), so unless you explicitly set it to something before using GL draw functions, the material can happen to be anything. Also, if you call any other drawing commands from inside GL drawing code, they can set material to something else, so make sure it's under control as well.

GL drawing commands execute immediately. That means if you call them in Update(), they will be executed before the camera is rendered (and the camera will most likely clear the screen, making the GL drawing not visible).

The usual place to call GL drawing is most often in OnPostRender() from a script attached to a camera

static var lineMaterial : Material;
static function CreateLineMaterial() {
    if( !lineMaterial ) {
        lineMaterial = new Material( "Shader \"Lines/Colored Blended\" {" +
            "SubShader { Pass { " +
            "    Blend SrcAlpha OneMinusSrcAlpha " +
            "    ZWrite Off Cull Off Fog { Mode Off } " +
            "    BindChannels {" +
            "      Bind \"vertex\", vertex Bind \"color\", color }" +
            "} } }" );
        lineMaterial.hideFlags = HideFlags.HideAndDontSave;
        lineMaterial.shader.hideFlags = HideFlags.HideAndDontSave;
    }
}
function OnPostRender() {
    CreateLineMaterial();
    // set the current material
    lineMaterial.SetPass( 0 );
    GL.Begin( GL.LINES );
    GL.Color( Color(1,1,1,0.5) );
    GL.Vertex3( 0, 0, 0 );
    GL.Vertex3( 1, 0, 0 );
    GL.Vertex3( 0, 1, 0 );
    GL.Vertex3( 1, 1, 0 );
    GL.Color( Color(0,0,0,0.5) );
    GL.Vertex3( 0, 0, 0 );
    GL.Vertex3( 0, 1, 0 );
    GL.Vertex3( 1, 0, 0 );
    GL.Vertex3( 1, 1, 0 );
    GL.End();
}

Note: This class is almost always used when you need to draw a couple of lines or triangles, and don't want to deal with meshes. If you want to avoid surprises the usage pattern is this:

function OnPostRender() {
     // Set your materials
     GL.PushMatrix();
     // yourMaterial.SetPass( );
     // Draw your stuff
     GL.PopMatrix();
}

Where at the "// Draw your stuff" you should do SetPass() on some material previously declared, which will be used for drawing. If you dont call SetPass, then you'll get basically a random material (whatever was used before) which is not good. So do it.

TRIANGLES	Mode for Begin: draw triangles.
TRIANGLE_STRIP	Mode for Begin: draw triangle strip.
QUADS	Mode for Begin: draw quads.
LINES	Mode for Begin: draw lines.
modelview	The current modelview matrix.
wireframe	Should rendering be done in wireframe?

Vertex3	Submit a vertex.
Vertex	Submit a vertex.
Color	Sets current vertex color.
TexCoord	Sets current texture coordinate (v.x,v.y,v.z) for all texture units.
TexCoord2	Sets current texture coordinate (x,y) for all texture units.
TexCoord3	Sets current texture coordinate (x,y,z) for all texture units.
MultiTexCoord2	Sets current texture coordinate (x,y) for the actual texture unit.
MultiTexCoord3	Sets current texture coordinate (x,y,z) to the actual texture unit.
MultiTexCoord	Sets current texture coordinate (v.x,v.y,v.z) to the actual texture unit.
Begin	Begin drawing 3D primitives.
End	End drawing 3D primitives.
LoadOrtho	Helper function to set up an ortho perspective transform.
LoadPixelMatrix	Setup a matrix for pixel-correct rendering.
Viewport	Set the rendering viewport.
LoadProjectionMatrix	Load an arbitrary matrix to the current projection matrix.
LoadIdentity	Load the identity matrix to the current modelview matrix.
MultMatrix	Multiplies the current modelview matrix with the one specified.
PushMatrix	Saves both projection and modelview matrices to the matrix stack.
PopMatrix	Restores both projection and modelview matrices off the top of the matrix stack.
GetGPUProjectionMatrix	Compute GPU projection matrix from camera's projection matrix.
SetRevertBackfacing	Select whether to invert the backface culling (true) or not (false).
Clear	Clear the current render buffer.
ClearWithSkybox	Clear the current render buffer with camera's skybox.
InvalidateState	Invalidate the internally cached renderstates.
IssuePluginEvent	Send a user-defined event to a native code plugin.