Category Archives: OpenGL

Omnidirectional shadows and VSDCT on OpenGL ES 3

Recently we have ported all the parts of our shading pipeline to OpenGL ES 3. The last piece of the puzzle was a decent implementation of omnidirectional shadow maps. We used a Virtual Shadow Depth Cube Texture (VSDCT) described in ShaderX3.

Here is a simple code snipped I wrote to convert cube map vec3 into a virtual texture vec2:

vec2 GetShadowTC( vec3 Dir )
{
	float Sc;
	float Tc;
	float Ma;
	float FaceIndex;

	float rx = Dir.x;
	float ry = Dir.y;
	float rz = Dir.z;

	vec3 adir = abs(Dir);
	Ma = max( max( adir.x, adir.y ), adir.z );

	if ( adir.x > adir.y && adir.x > adir.z )
	{
		Sc = ( rx > 0.0 ) ? rz : -rz;
		Tc = ry;
		FaceIndex = ( rx > 0.0 ) ? 0.0 : 1.0;
	}
	else if ( adir.y > adir.x && adir.y > adir.z )
	{
		Sc = rx;
		Tc = ( ry > 0.0 ) ? rz : -rz;
		FaceIndex = ( ry > 0.0 ) ? 2.0 : 3.0;
	}
	else
	{
		Sc = ( rz > 0.0 ) ? -rx : rx;
		Tc = ry;
		FaceIndex = ( rz > 0.0 ) ? 4.0 : 5.0;
	}

	float s = 0.5 * ( Sc / Ma + 1.0 );
	float t = 0.5 * ( Tc / Ma + 1.0 );

	s = s / 3.0;
	t = t / 2.0;

	float Flr = floor(FaceIndex / 3.0);
	float Rmd = FaceIndex - (3.0 * Flr);

	s += Rmd / 3.0;
	t += Flr / 2.0;

	return vec2( s, t );
}

The distance from the light source is packed into a 8-bit RGBA texture using this trick. Everything else is pretty straightforward.

Android demo (requires OpenGL ES 3).

Vertex Array Object (VAO) on Android

Always wanted to put my hands on an OpenGL ES 3 Android device. Here are the results of testing VAO on Google Nexus 10 (Android 4.3 with OpenGL ES 3) and Samsung Galaxy Nexus (Android 4.3 with OpenGL ES 2 and OES_vertex_array_object extension).

1. First, the old Samsung Galaxy Nexus. 
The extensions list claims the OES_vertex_array_object extension is supported. So, I load the entry points:

#define BIND_EXT( VarName, Type, Bind1, Bind2 )\
        VarName = (Type)GetGLProc( API, Bind1 );\
        if ( !VarName ) VarName = (Type)GetGLProc( API, Bind2 );
BIND_EXT( API->glBindVertexArray,
          PFNGLBINDVERTEXARRAYPROC,
          "glBindVertexArray", "glBindVertexArrayOES" );
BIND_EXT( API->glDeleteVertexArrays,
          PFNGLDELETEVERTEXARRAYSPROC,
          "glDeleteVertexArrays", "glDeleteVertexArraysOES" );
BIND_EXT( API->glGenVertexArrays,
          PFNGLGENVERTEXARRAYSPROC,
          "glGenVertexArrays", "glGenVertexArraysOES" );

Just in case, I check for the presence of actual functions.

bool IsVAOSupported = API->glBindVertexArray &&
                      API->glDeleteVertexArrays &&
                      API->glGenVertexArrays;

It looks fine, so we start rendering using VAO in hope everything will go as expected. Nope, it doesn’t:

E/libEGL: called unimplemented OpenGL ES API.

Pfff, stop saying “Yes, we support VAO!”.

2. Here goes the Google Nexus 10 (with an awesome 2560×1600 10-inch touchscreen).

I/LEngine: OpenGL version   : OpenGL ES 3.0
I/LEngine: OpenGL vendor    : ARM
I/LEngine: OpenGL renderer  : Mali-T604
I/LEngine: GLSL version     : OpenGL ES GLSL ES 3.00

VAO just works using the same code path, which is used on a desktop OpenGL 3.2.