darling-cocotron/Onyx2D/O2Paint_radialGradient.m

/*------------------------------------------------------------------------
 *
 * Derivative of the OpenVG 1.0.1 Reference Implementation
 * -------------------------------------
 *
 * Copyright (c) 2007 The Khronos Group Inc.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and /or associated documentation files
 * (the "Materials "), to deal in the Materials without restriction,
 * including without limitation the rights to use, copy, modify, merge,
 * publish, distribute, sublicense, and/or sell copies of the Materials,
 * and to permit persons to whom the Materials are furnished to do so,
 * subject to the following conditions: 
 *
 * The above copyright notice and this permission notice shall be included 
 * in all copies or substantial portions of the Materials. 
 *
 * THE MATERIALS ARE PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
 * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
 * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE MATERIALS OR
 * THE USE OR OTHER DEALINGS IN THE MATERIALS.
 *
 *-------------------------------------------------------------------*/
#import <Onyx2D/O2Paint_radialGradient.h>
#import <Onyx2D/O2Shading.h>

@implementation O2Paint_radialGradient

ONYX2D_STATIC_INLINE void quadratic(O2Float a, O2Float hb, O2Float c, O2Float *x1, O2Float *x2) {
	// Solve a*x*x + 2*hb*x + c = 0 numerically, trying not to lose precision
	// for cases when a is close to 0.
	O2Float qD = hb*hb - a * c;
	O2Float d = (O2Float) sqrt(qD);
	*x1 = c / (-hb + d);
	*x2 = c / (-hb - d);
}

void O2PaintRadialGradient(O2Paint_radialGradient *self,O2Float *g, O2Float *rho, O2Float x, O2Float y) {
	RI_ASSERT(self);
	if( self->_endRadius <= 0.0f )
	{
		*g = 1.0f;
		*rho = 0.0f;
		return;
	}

	O2Point gx = O2PointMake(self->m_surfaceToPaintMatrix.a, self->m_surfaceToPaintMatrix.b);
	O2Point gy = O2PointMake(self->m_surfaceToPaintMatrix.c, self->m_surfaceToPaintMatrix.d);

	O2Float r = self->_endRadius;
	O2Float R = self->_startRadius;

	O2Point O = self->_endPoint;

	O2Point p = O2PointMake(x, y);
	p = Vector2Subtract(O2PointApplyAffineTransform(p, self->m_surfaceToPaintMatrix), O);

	O2Point f = self->_startPoint;
	f = Vector2Subtract(f, O);

	O2Point d = Vector2Subtract(p, f);
	O2Float dd = Vector2Dot(d, d);
	O2Float df = Vector2Dot(d, f);
	O2Float ff = Vector2Dot(f, f);

	O2Float a = ff - r*r - R*R + 2*r*R;
	O2Float hb = df + R*R - R*r;
	O2Float c = dd - R*R;

	*rho = 0.01; // TODO: something smarter

	O2Float g_inside, g_outside;
	quadratic(a, hb, c, &g_inside, &g_outside);

	BOOL outsideVisible = (self->_extendStart || 0.0 <= g_outside - *rho)
	                     && (self->_extendEnd || g_outside + *rho <= 1.0)
                             && (a >= 0.0 || R > r);
	*g = outsideVisible? g_outside : g_inside;

	O2Float resultingRadius = (R * (1 - *g)) + (*g * r);
	if (resultingRadius < 0.0) {
		*g = NAN;
	}
}


ONYX2D_STATIC_INLINE O2argb32f radialGradientColorAt(O2Paint_radialGradient *self,int x,int y,int *skip){
   O2argb32f result;
   
   O2Float g, rho;
   O2PaintRadialGradient(self,&g, &rho, x+0.5f, y+0.5f);

   result = O2PaintColorRamp(self,g, rho,skip);

   return result;
}

ONYX2D_STATIC int radial_span_largb8u_PRE(O2Paint *selfX,int x,int y,O2argb8u *span,int length){
   O2Paint_radialGradient *self=(O2Paint_radialGradient *)selfX;
   int i;
   int previous=-1;
   
   for(i=0;i<length;i++,x++){
    int skip=0;
    O2argb32f value=radialGradientColorAt(self,x,y,&skip);
    
    if(skip!=previous){
     if(previous==-1)
      previous=skip;
     else
      return (previous==1)?-i:i;
    }
    
    span[i]=O2argb8uFromO2argb32f(value);
   }
   return (previous==1)?-length:length;
}

ONYX2D_STATIC int radial_span_largb32f_PRE(O2Paint *selfX,int x,int y,O2argb32f *span,int length){
   O2Paint_radialGradient *self=(O2Paint_radialGradient *)selfX;
   int i;
   int previous=-1;
   
   for(i=0;i<length;i++,x++){
    int skip=0;
    O2argb32f value=radialGradientColorAt(self,x,y,&skip);
    
    if(skip!=previous){
     if(previous==-1)
      previous=skip;
     else
      return (previous==1)?-i:i;
    }
    
    span[i]=value;
   }
   return (previous==1)?-length:length;
}

-initWithShading:(O2Shading *)shading deviceTransform:(O2AffineTransform)deviceTransform {
   [super initWithShading:shading deviceTransform:deviceTransform numberOfSamples:1024];
   _paint_largb8u_PRE=radial_span_largb8u_PRE;
   _paint_largb32f_PRE=radial_span_largb32f_PRE;
   _startRadius=[shading startRadius];
   _endRadius=[shading endRadius];

   return self;
}


@end