4advect.fs

#version 460 core
in vec2 TexCoords;
uniform sampler2D olduv;//tex1
uniform float gridsize;
out vec3 uv1;
//layout(location=1) out vec3 uv2
//timestep 0.1  rdx 1
//this advect shader is to advect velocity
//take uv0 GL_TEXTURE0 as input (old uv) 
//and store the output in uv1, the color_attachment0 of uvfb
//dt=0.8 advect.fs force.fs µÄʱ¼äÐèÒªÒ»ÖÂ
void main()
{
	float dt=0.02;//0.04
	//vec2 v1=vec2(texture(olduv,TexCoords));// v1=velocity(p)
	//vec2 pos=vec2(gl_FragCoord.x,gl_FragCoord.y);
	//vec2 oldpos=pos-0.5*dt*1.0*vec2(texture(olduv,TexCoords));//find p1
	//vec2 oldtexcoord=vec2((oldpos.x-0.5)/799.0,(oldpos.y-0.5)/599.0);
	
	


	//oldtexcoord=vec2(oldpos.x/800.0,oldpos.y/600.0);
	//oldtexcoord=vec2(oldpos.x/800.0,oldpos.y/800.0);
	//vec2 v2=vec2(texture(olduv,oldtexcoord));//v2=velocity(p1)
	
	//oldpos=pos-0.75*dt*v2;//find p2
	
	//oldtexcoord=vec2(oldpos.x/800.0,oldpos.y/600.0);
	//oldtexcoord=vec2(oldpos.x/800.0,oldpos.y/800.0);
	//vec2 v3=vec2(texture(olduv,oldtexcoord));//v3=velocity(p2)
	//oldpos=pos-dt*(2.0/9.0*v1+1.0/3.0*v2+4.0/9.0*v3);
	
	//oldtexcoord=vec2(oldpos.x/800.0,oldpos.y/600.0);
	//oldtexcoord=vec2(oldpos.x/800.0,oldpos.y/800.0);
	//uv1=vec3(texture(olduv,oldtexcoord));
	//uv1=vec3(texture(olduv,TexCoords));//to test force.fs 

	vec2 v1=vec2(texture(olduv,TexCoords));
	
	vec2 offset=0.5*dt/gridsize*v1;
	//vec2 offset=0.5*dt/800*v1;

	vec2 v2=vec2(texture(olduv,TexCoords-offset));

	
	offset=0.75*dt/gridsize*v2;
	//offset=0.75*dt/800*v2;
	vec2 v3=vec2(texture(olduv,(TexCoords-offset)));

	
	offset=dt/gridsize*(2.0/9.0*v1+1.0/3.0*v2+4.0/9.0*v3);
	//offset=dt/800*(2.0/9.0*v1+1.0/3.0*v2+4.0/9.0*v3);
	uv1=vec3(texture(olduv,TexCoords-offset))*0.9995;

}