Circle of Quads

QuadCircle.cpp

#include "cinder/app/App.h"
#include "cinder/app/RendererGl.h"
#include "cinder/gl/gl.h"

#include "cinder/Camera.h"
#include "cinder/CameraUi.h"
#include "cinder/ip/Checkerboard.h"

using namespace ci;
using namespace ci::app;

struct Quad {
	mat4 transform;

	Quad( const vec3 &position )
	{
		vec3 scale = vec3( 100 );
		vec3 target = vec3( 0 );
		vec3 up = vec3( 0, 1, 0 );

		transform = glm::translate( position );

		// Instead of glm::lookAt, we can simply create a rotation from the default orientation
		// (looking down the positive Z-axis) to the desired one (looking at the target).
		// The glm::rotation() method creates a quaternion which we can convert to a mat4 and
		// apply to our transform.
		transform *= glm::toMat4( glm::rotation( vec3( 0, 0, 1 ), glm::normalize( target - position ) ) );

		transform *= glm::scale( scale );
	}
};

class QuadCircle : public App {
  public:
	static void init( App::Settings *settings );

	void setup() override;
	void draw() override;

	gl::TextureRef _texture;

	std::vector<Quad> _quads;
	gl::BatchRef      _quadBatch;

	CameraPersp _camera;
	CameraUi    _camUi;
};

void QuadCircle::init( App::Settings *settings )
{
	settings->setWindowSize( 1280, 720 );
}

void QuadCircle::setup()
{
	const int    num_quads = 12;
	const double radius = 250.0f;

	for( auto i = 0; i < num_quads; i++ ) {
		double angle = (double)i * 2.0f * M_PI / num_quads;
		double x = cos( angle ) * radius;
		double y = 0;
		double z = sin( angle ) * radius;
		vec3   pos = vec3( x, y, z );

		_quads.emplace_back( pos );
	}

	_camera = CameraPersp( getWindowWidth(), getWindowHeight(), 60.0f, 0.1f, 1000.0f );
	_camera.lookAt( vec3( 0, 0, radius ), vec3( 0 ) );

	_camUi = CameraUi( &_camera, getWindow() );

	_texture = gl::Texture::create( ip::checkerboard( 1024, 1024, 128 ) );

	_quadBatch = gl::Batch::create(
	    geom::Rect().rect( Rectf( -0.5, -0.5, 0.5, 0.5 ) ),
	    gl::getStockShader( gl::ShaderDef().color().texture() ) );
}

void QuadCircle::draw()
{
	gl::ScopedColor       scpColor( Color( 0.8f, 0.8f, 0.3f ) );
	gl::ScopedTextureBind scpTex0( _texture );
	gl::ScopedDepth       scpDepth( true );
	gl::ScopedFaceCulling scpCull( true );
	gl::ScopedMatrices    scpMatrices;

	gl::clear( Color( 0.0f, 0.0f, 0.0f ) );
	gl::setMatrices( _camera );
	
	for( auto &q : _quads ) {
		gl::setModelMatrix( q.transform );
		_quadBatch->draw();
	}
}

CINDER_APP( QuadCircle, RendererGl, QuadCircle::init )