VERC: Painlessly Drawing TriAPI In Orthogonal Mode Last edited 3 years ago2019-04-17 10:35:36 UTC

Orthogonal Triangle Renderering inside The Half-Life SDK

I decided to whip up this tutorial to show you the simplicity of drawing triangles in orthogonal mode using TriAPI. This is really simple, and I'm even doing all the work for you! An example regarding how to draw a quad over the entire screen is included at the end of the article.

Step #1

Load up tri.cpp and add this shell at the very bottom:
Orthogonal Triangles -- (relative to resolution,
smackdab on the screen) add them here
void HUD_DrawOrthoTriangles( void )

Step #2

Open up HUD_Redraw.cpp, and prototype the function above redraw():
void HUD_DrawOrthoTriangles( void );
int CHud :: Redraw( float flTime, int intermission )

Step #3

Add the function inside redraw, so it's called. HUD_DrawOrthoTriangles is called from the HUD draw functions, because at this point the engine is already in orthogonal mode. Hence, the Z coord is a "magic 0", because it's not rendering in world space in ortho, it's 2D.
          pList = pList->pNext;

//omega;draw orthogonal triangles

// are we in demo mode? do we need to
// draw the logo in the top corner?
if (m_iLogo)

Step #4

Make use of it! Example:
void OrthoExample()
    gEngfuncs.pTriAPI->RenderMode(kRenderTransAdd); //additive

    // use hotglow, or any other sprite for the texture
    gEngfuncs.pTriAPI->SpriteTexture( (struct model_s *)

    gEngfuncs.pTriAPI->CullFace( TRI_NONE ); //no culling
    gEngfuncs.pTriAPI->Begin(TRI_QUADS); //start our quad

    //remember, always list vertices in counter-clockwise
    // order, unless you want the quad to be backwards =)
    // the third value of vertex3f will always be 0 in ortho mode,
    // don't change it unless you wan't funny things to happen.

    //top left
    gEngfuncs.pTriAPI->TexCoord2f(0.0f, 1.0f);
    gEngfuncs.pTriAPI->Vertex3f(0, 0, 0);

    //bottom left
    gEngfuncs.pTriAPI->TexCoord2f(0.0f, 0.0f);
    gEngfuncs.pTriAPI->Vertex3f(0, ScreenHeight, 0);

    //bottom right
    gEngfuncs.pTriAPI->TexCoord2f(1.0f, 0.0f);
    gEngfuncs.pTriAPI->Vertex3f(ScreenWidth, ScreenHeight, 0);

    //top right
    gEngfuncs.pTriAPI->TexCoord2f(1.0f, 1.0f);
    gEngfuncs.pTriAPI->Vertex3f(ScreenWidth, 0, 0);

    gEngfuncs.pTriAPI->End(); //end our list of vertexes
    gEngfuncs.pTriAPI->RenderMode(kRenderNormal); //return to normal
void HUD_DrawOrthoTriangles( void )
That about does it for this "tutorial". You now have the framework to draw triangles onto the hud with ease using TriAPI. Have fun, and enjoy! If you have any questions, email me at

This article was originally published on the Valve Editing Resource Collective (VERC).
TWHL only archives articles from defunct websites. For more information on TWHL's archiving efforts, please visit the TWHL Archiving Project page.


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