/**
Created by Alex Neville
Language: GLSL for Shadertoy

	PhotoAlter: A shader that continually changes an image from the following 
		four settings:
        1. Color
        2. Grayscale
        3. Sepia
        4. Negative
**/

#define PI 3.1415926535897932384626433832795
#define PI_T PI / 2.0
#define T_PI PI * 2.0
#define ALPHA 255.0
#define SCALE 1.0

/**
	MainImage method: Controls the color value of each pixel.
		This is based on a function of the current time,
		two sine wave, and the unit circle. 
**/
void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
	vec2 xy = fragCoord.xy / iResolution.xy;
    xy.y = SCALE - xy.y;
    vec4 textureColor = texture(iChannel0, xy);
    
    // obtain elapsed time in seconds
    float timeWave1 = sin(iTime);
    float timeWave2 = sin(iTime*2.0);
    
    // Color: Keep as is. Sin(0) = 0. 
    if (timeWave1 >= 0.0 && timeWave2 >= 0.0)
    {
		;
    }
    // Black and White:
    else if (timeWave1 >= 0.0 && timeWave2 < 0.0)
    {
     	textureColor.rgb = vec3(0.21 * textureColor.r + 0.72 *
            textureColor.g + 0.07 * textureColor.b);
    }
    // Sepia:
    else if (timeWave1 < 0.0 && timeWave2 >= 0.0)
    {
        float tr = 0.393 * textureColor.r + 0.769 * textureColor.g
            + 0.189 * textureColor.b;
        float tg = 0.349 * textureColor.r + 0.686 * textureColor.g
            + 0.168 * textureColor.b;
        float tb = 0.272 * textureColor.r + 0.534 * textureColor.g
            + 0.131 * textureColor.b;
        if (tr > ALPHA)
        {
            textureColor.r = ALPHA;
        }
        else
        {
            textureColor.r = tr;
        }
        if (tg > ALPHA)
        {
            textureColor.g = ALPHA;
        }
        else
        {
            textureColor.g = tg;
        }
        if (tb > ALPHA)
        {
            textureColor.b = ALPHA;
        }
        else
        {
            textureColor.b = tb;
        }
    }
    // Negative: Use 1.0, not 255.0, for this scaling!
    else
    {
        float tr = SCALE - textureColor.r;
        float tg = SCALE - textureColor.g;
        float tb = SCALE - textureColor.b;
        textureColor.r = tr;
        textureColor.g = tg;
        textureColor.b = tb;
    }
    fragColor = textureColor;
}