Generate pixel bounds for Cinder Texture #pixelbounds #cinder #opengl #texture #collision-detection

PixelBounds.cpp

//
//  PixelBounds.cpp
//  Demonstrates calculating the actual pixel bounds ( non-transparent bounds ) for a texture in Cinder
//  More information here: http://wp.me/pPFvc-42
//

#include <cinder/app/AppBasic.h>
#include <cinder/Font.h>
#include <cinder/Text.h>
#include "cinder/gl/Texture.h"
#include "cinder/Surface.h"
#include "cinder/Area.h"
#include "Resources.h"

using namespace ci;
using namespace ci::app;
using namespace ci::gl;

class PixelBounds : public AppBasic 
{
 public:
	
	void prepareSettings( Settings *settings );
	void setup();
	void draw();
	
	Font font;
	TextLayout layout;
	Texture texture;
	Surface8u surface;
	Area pixelBounds;
	
};

void PixelBounds::prepareSettings( Settings *settings )
{
	settings->setWindowSize( 620, 150 );
	settings->setFrameRate( 60.0f );
	settings->setResizable( true );
	settings->setFullScreen( false );
}

void PixelBounds::setup()
{
	// -- create the font and set up the TextLayout
	font = Font( loadResource( RES_FONT_METROPOLIS ), 118 );
	layout.setFont( font );
	layout.setColor( ColorA( 1.0f, 1.0f, 1.0f, 1.0f ) );
	layout.addLine( "Pixel Bounds" );
	
	surface = layout.render( true, false );
	texture = Texture( surface );
	
	// -- using surface.getBounds() causes problems
	// -- so use texture.getCleanBounds();
	Area bounds = texture.getCleanBounds();
	Surface::Iter iter = surface.getIter( bounds );
	
	// -- begin by inverting a bounding box
	// -- set the corners of the area to the max and min pixels possible
	pixelBounds.x1 = bounds.x2;
	pixelBounds.y1 = bounds.y2;
	pixelBounds.y2 = bounds.y1;
	pixelBounds.x2 = bounds.x1;

	while( iter.line() ) 
	{
		while( iter.pixel() ) 
		{
			int x = 0;
			int y = 0;
			
			// -- if the alpha channel of the current pixel is greater than zero
			if (iter.a() > 0 ) 
			{
				// -- iter.getPos() does not traverse the pixels as you might expect
				// -- it's possible that the x and y points will start near the middle of the texture
				x = iter.getPos().x;
				y = iter.getPos().y;
				
				// -- if the non-transparent pixel is out of the bounds of the respective area x,y
				// -- set the area to the current pixel's x,y coords
				pixelBounds.x1 = std::min( x, pixelBounds.x1 );
				pixelBounds.y1 = std::min( y, pixelBounds.y1 );
				pixelBounds.x2 = std::max( x, pixelBounds.x2 );
				pixelBounds.y2 = std::max( y, pixelBounds.y2 );
			}
		}
	}
}


void PixelBounds::draw()
{
	gl::clear( Color( 0.1f, 0.1f, 0.1f ) );
	gl::enableAlphaBlending();
	gl::pushMatrices();
	gl::translate( Vec2i( 10, 10 ) );
	
	// -- draw the texture bounds
	gl::color( ColorA( 1.0f, 1.0f, 1.0f, 1.0f ) );
	gl::drawSolidRect( texture.getBounds() );
	
	// -- draw pixel bounds
	gl::color( ColorA( 0.0f, 0.80f, 1.0f, 1.0f ) );
	gl::drawSolidRect( pixelBounds );
	
	// -- draw the texture
	gl::color( ColorA( 0.97f, 0.14f, 0.4f, 1.0f ) );
	gl::draw( texture );
	gl::popMatrices();
	gl::disableAlphaBlending();
}

CINDER_APP_BASIC( PixelBounds, RendererGl )