ihealth_ios/Inhealth/HSBSupport.m

//==============================================================================
//
//  HSBSupport
//  HSBSupport
//
//  Created by Troy Gaul on 7 Aug 2010.
//
//  Copyright (c) 2011-2013 InfinitApps LLC: http://infinitapps.com
//	Some rights reserved: http://opensource.org/licenses/MIT
//
//==============================================================================

#import "HSBSupport.h"

//------------------------------------------------------------------------------

float pin(float minValue, float value, float maxValue)
{
	if (minValue > value)
		return minValue;
	else if (maxValue < value)
		return maxValue;
	else
		return value;
}

//------------------------------------------------------------------------------
#pragma mark	Floating point conversion
//------------------------------------------------------------------------------

static void hueToComponentFactors(float h, float* r, float* g, float* b)
{
	float h_prime = h / 60.0f;
	float x = 1.0f - fabsf(fmodf(h_prime, 2.0f) - 1.0f);
	
	if (h_prime < 1.0f) {
		*r = 1;
		*g = x;
		*b = 0;
	}
	else if (h_prime < 2.0f) {
		*r = x;
		*g = 1;
		*b = 0;
	}
	else if (h_prime < 3.0f) {
		*r = 0;
		*g = 1;
		*b = x;
	}
	else if (h_prime < 4.0f) {
		*r = 0;
		*g = x;
		*b = 1;
	}
	else if (h_prime < 5.0f) {
		*r = x;
		*g = 0;
		*b = 1;
	}
	else {
		*r = 1;
		*g = 0;
		*b = x;
	}
}

//------------------------------------------------------------------------------

void HSVtoRGB(float h, float s, float v, float* r, float* g, float* b)
{
	hueToComponentFactors(h, r, g, b);
	
	float c = v * s;
	float m = v - c;
	
	*r = *r * c + m;
	*g = *g * c + m;
	*b = *b * c + m;
}

//------------------------------------------------------------------------------

void RGBToHSV(float r, float g, float b, float* h, float* s, float* v, BOOL preserveHS)
{
	float max = r;
	
	if (max < g)
		max = g;
	
	if (max < b)
		max = b;
	
	float min = r;
	
	if (min > g)
		min = g;
	
	if (min > b)
		min = b;
	
	// Brightness (aka Value)
	
	*v = max;
	
	// Saturation
	
	float sat;
	
	if (max != 0.0f) {
		sat = (max - min) / max;
		*s = sat;
	}
	else {
		sat = 0.0f;
		
		if (!preserveHS)
			*s = 0.0f;                                      // Black, so sat is undefined, use 0
	}
	
	// Hue
	
	float delta;
	
	if (sat == 0.0f) {
		if (!preserveHS)
			*h = 0.0f;                                      // No color, so hue is undefined, use 0
	}
	else {
		delta = max - min;
		
		float hue;
		
		if (r == max)
			hue = (g - b) / delta;
		else if (g == max)
			hue = 2 + (b - r) / delta;
		else
			hue = 4 + (r - g) / delta;
		
		hue /= 6.0f;
		
		if (hue < 0.0f)
			hue += 1.0f;
		
		if (!preserveHS || fabsf(hue - *h) != 1.0f)
			*h = hue;                               // 0.0 and 1.0 hues are actually both the same (red)
	}
}

//------------------------------------------------------------------------------
#pragma mark	Square/Bar image creation
//------------------------------------------------------------------------------

static UInt8 blend(UInt8 value, UInt8 percentIn255)
{
	return (UInt8) ((int) value * percentIn255 / 255);
}

//------------------------------------------------------------------------------

static CGContextRef createBGRxImageContext(int w, int h, void* data)
{
	CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
	
	CGBitmapInfo kBGRxBitmapInfo = kCGBitmapByteOrder32Little | kCGImageAlphaNoneSkipFirst;
	// BGRA is the most efficient on the iPhone.
	
	CGContextRef context = CGBitmapContextCreate(data, w, h, 8, w * 4, colorSpace, kBGRxBitmapInfo);
	
	CGColorSpaceRelease(colorSpace);
	
	return context;
}

//------------------------------------------------------------------------------

CGImageRef createSaturationBrightnessSquareContentImageWithHue(float hue)
{
	void* data = malloc(256 * 256 * 4);
	if (data == nil)
		return nil;
	
	CGContextRef context = createBGRxImageContext(256, 256, data);
	
	if (context == nil) {
		free(data);
		return nil;
	}
	
	UInt8* dataPtr = data;
	size_t rowBytes = CGBitmapContextGetBytesPerRow(context);
	
	float r, g, b;
	hueToComponentFactors(hue, &r, &g, &b);
	
	UInt8 r_s = (UInt8) ((1.0f - r) * 255);
	UInt8 g_s = (UInt8) ((1.0f - g) * 255);
	UInt8 b_s = (UInt8) ((1.0f - b) * 255);
	
	for (int s = 0; s < 256; ++s) {
		register UInt8* ptr = dataPtr;
		
		register unsigned int r_hs = 255 - blend(s, r_s);
		register unsigned int g_hs = 255 - blend(s, g_s);
		register unsigned int b_hs = 255 - blend(s, b_s);
		
		for (register int v = 255; v >= 0; --v) {
			ptr[0] = (UInt8) (v * b_hs >> 8);
			ptr[1] = (UInt8) (v * g_hs >> 8);
			ptr[2] = (UInt8) (v * r_hs >> 8);
			
			// Really, these should all be of the form used in blend(),
			// which does a divide by 255. However, integer divide is
			// implemented in software on ARM, so a divide by 256
			// (done as a bit shift) will be *nearly* the same value,
			// and is faster. The more-accurate versions would look like:
			//	ptr[0] = blend(v, b_hs);
			
			ptr += rowBytes;
		}
		
		dataPtr += 4;
	}
	
	// Return an image of the context's content:
	
	CGImageRef image = CGBitmapContextCreateImage(context);
	
	CGContextRelease(context);
	free(data);
	
	return image;
}

//------------------------------------------------------------------------------

CGImageRef createHSVBarContentImage(InfComponentIndex barComponentIndex, float hsv[3])
{
	UInt8 data[256 * 4];
	
	// Set up the bitmap context for filling with color:
	
	CGContextRef context = createBGRxImageContext(256, 1, data);
	
	if (context == nil)
		return nil;
	
	// Draw into context here:
	
	UInt8* ptr = CGBitmapContextGetData(context);
	if (ptr == nil) {
		CGContextRelease(context);
		return nil;
	}
	
	float r, g, b;
	for (int x = 0; x < 256; ++x) {
		hsv[barComponentIndex] = (float) x / 255.0f;
		
		HSVtoRGB(hsv[0] * 360.0f, hsv[1], hsv[2], &r, &g, &b);
		
		ptr[0] = (UInt8) (b * 255.0f);
		ptr[1] = (UInt8) (g * 255.0f);
		ptr[2] = (UInt8) (r * 255.0f);
		
		ptr += 4;
	}
	
	// Return an image of the context's content:
	
	CGImageRef image = CGBitmapContextCreateImage(context);
	
	CGContextRelease(context);
	
	return image;
}

//------------------------------------------------------------------------------