无法在OpenGL中绘制三角形，但其他图元可以很好地渲染

Question

Good afternoon,

I'm trying to learn to use a graphics library that uses OpenGL. I can draw 2D primitives (text and lines) but 3D triangles don't render. I've tried everything I can think of but as an OpenGL newcomer I've probably missed something obvious.

This code is not intended to be efficient. I'm trying to get it to work first.

Here's the setup at startup:

  // 800 by 600 windows 32 bit depth
  Driver->setDisplay( UDriver::CMode( ScreenWidth, ScreenHeight, 32 ) );
  NL3D::CViewport viewport;
  viewport.initFullScreen();
  Driver->setViewport( viewport );

  NLMISC::CMatrix mtx;
  mtx.identity();
  Driver->setViewMatrix( mtx );
  Driver->setModelMatrix( mtx );

  // screen size is same as pixel resolution
  // CFrustum(float left, float right, float bottom, float top, float znear, float zfar, bool perspective= true)
  Driver->setMatrixMode2D( CFrustum( 0.0f, ScreenWidth, 0.0f, ScreenHeight, -2.0f, 10000.0f, false ) );

Here's the code in my rendering loop:

static NL3D::CMaterial mat;
mat.initUnlit();
mat.setColor( CRGBA( 255, 255, 0, 128 ) );

float x = 200.0f;
float y = 200.0f;
float width = 200.0f; // (float)ScreenWidth * 0.125f;
float height = 200.0f; // (float)ScreenHeight * 0.125f;
static NL3D::CVertexBuffer vb;
if ( vb.getName().empty() )
   vb.setName("drawBitmap");
vb.setVertexFormat( NL3D::CVertexBuffer::PositionFlag | NL3D::CVertexBuffer::TexCoord0Flag );
vb.setNumVertices( 4 );
{
   NL3D::CVertexBufferReadWrite vba;
   vb.lock( vba );
   vba.setVertexCoord( 0, NLMISC::CVector( x, 0, y ) );
   vba.setVertexCoord( 1, NLMISC::CVector( x + width, 0, y ) );
   vba.setVertexCoord( 2, NLMISC::CVector( x + width, 0, y + height ) );
   vba.setVertexCoord( 3, NLMISC::CVector( x, 0, y + height ) );
   vba.setTexCoord( 0, 0, 0.f, 1.f );
   vba.setTexCoord( 1, 0, 1.f, 1.f );
   vba.setTexCoord( 2, 0, 1.f, 0.f );
   vba.setTexCoord( 3, 0, 0.f, 0.f );
}
dynamic_cast<NL3D::CDriverUser*>(Driver)->getDriver()->activeVertexBuffer( vb );

static NL3D::CIndexBuffer pb;
if ( pb.getName().empty() )
   pb.setName("drawBitmap");
pb.setFormat( NL_DEFAULT_INDEX_BUFFER_FORMAT );
pb.setNumIndexes( 6 );
{
   CIndexBufferReadWrite iba;
   pb.lock( iba );
   iba.setTri( 0, 0, 1, 2 );
   iba.setTri( 3, 2, 3, 0 );
}

dynamic_cast<NL3D::CDriverUser*>(Driver)->getDriver()->activeIndexBuffer( pb );
dynamic_cast<NL3D::CDriverUser*>(Driver)->getDriver()->renderTriangles( mat, 0, 2 );

Any suggestions?

Thanks

Answer 1

It turned out to be multiple OpenGL contexts. It wasn't setting things back before trying to draw.