fluid2d.txt

// | - v - |
// u   s   u
// | - v - |

uniform vec2 scale_inv;

/////////////////////////////////////////
vec4 value4( sampler2D F, vec2 p ) {
	return texture2D( F, p * scale_inv );
}

vec2 value2( sampler2D F, vec2 p ) {
	return texture2D( F, p * scale_inv ).xy;
}

vec value( sampler2D F, vec2 p ) {
	return texture2D( F, p * scale_inv ).x;
}

vec value_x( sampler2D F, vec2 p ) {
	return texture2D( F, p * scale_inv ).x;
}

vec value_y( sampler2D F, vec2 p ) {
	return texture2D( F, p * scale_inv ).y;
}

/////////////////////////////////////////
vec4 advect( sampler2D F, sampler2D U, vec2 p, float dt ) {
	vec2 u = value2( U, p );

	return value4( F, p - u * dt ); // higher order
}

vec2 force( sampler2D U, vec2 p, float acc, float dt ) {
	vec2 u = value2( U, p );

	return u + acc * dt;
}

vec4 jacobi( sampler2D F, sampler2D G, vec2 p, vec2 e ) {
	vec4 f_l = value4( F, p + vec2( -1.0, 0.0 ) );
	vec4 f_r = value4( F, p + vec2( +1.0, 0.0 ) );
	vec4 f_b = value4( F, p + vec2( 0.0, -1.0 ) );
	vec4 f_t = value4( F, p + vec2( 0.0, +1.0 ) );

	vec4 g = value4( G, p );

	return ( f_l + f_r + f_b + f_t + g * e.x ) * e.y;
}

float div( sampler2D F, vec2 p ) {
	float x_l = value_x( F, p + vec2( -1.0, 0.0 ) );
	float x_r = value_x( F, p + vec2( +1.0, 0.0 ) );
	float y_b = value_y( F, p + vec2( 0.0, -1.0 ) );
	float y_t = value_y( F, p + vec2( 0.0, +1.0 ) );

	return ( ( x_r - x_l ) + ( y_t - y_b ) ) * 0.5;
}

vec2 grad( sampler2D F, vec2 p ) {
	float f_l = value( F, p + vec2( -1.0, 0.0 ) );
	float f_r = value( F, p + vec2( +1.0, 0.0 ) );
	float f_b = value( F, p + vec2( 0.0, -1.0 ) );
	float f_t = value( F, p + vec2( 0.0, +1.0 ) );

	return vec2( f_r - f_l, f_t - f_b ) * 0.5;
}

/////////////////////////////////////////
#ifdef PASS_ADVERT
uniform sampler2D F, U;
uniform float dt;

void main( void ) {
	vec2 p = gl_FragCoord.xy;

	gl_FragColor = advert( F, U, p, dt );
}
#endif

/////////////////////////////////////////
#ifdef PASS_FORCE
uniform sampler2D U;
uniform float acc, dt;

void main( void ) {
	vec2 p = gl_FragCoord.xy;

	gl_FragColor = vec4( force( U, p, acc, dt ), 0.0, 0.0 );
}
#endif

/////////////////////////////////////////
#ifdef PASS_DIV
uniform sampler2D U;

void main( void ) {
	vec2 p = gl_FragCoord.xy;

	gl_FragColor = vec4( div( U, p ) );
}
#endif

/////////////////////////////////////////
#ifdef PASS_JACOBI
uniform sampler2D F, G;
vec2 e;

void main( void ) {
	vec2 p = gl_FragCoord.xy;

	gl_FragColor = jacobi( F, G, p, e );
}
#endif

/////////////////////////////////////////
#ifdef PASS_GRAD
uniform sampler2D F, U;
vec2 e;

void main( void ) {
	vec2 p = gl_FragCoord.xy;

	gl_FragColor = vec4( value2( F, p ) - grad( U, p ), 0.0, 0.0 );
}
#endif