src/shaders/updateVelocityShader.comp

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#version 430

layout(local_size_x = 16, local_size_y = 16) in; 

layout  (std430,binding = 4) readonly buffer height0 
{
    float water0[];
    
};

layout (std430, binding = 5) readonly buffer height1
{
    float water1[]; 
};

//Since in previous step, (advectVelocity) we used this as inbuffer and vxout as out. Now we are interested in the new data and want to save it to a out buffer. vin cotains nothing of value anymore. use it as out data. DO NOT SWAP IN CPP.

layout (std430,binding = 6) writeonly buffer velocityX 
{
    float vxin[];
    
};

layout (std430,binding = 7) readonly buffer velocityXout 
{
    float vxout[];
    
};


layout (std430,binding = 8) writeonly buffer velocityY 
{   
    float vyin[];
    
};


layout (std430,binding = 9) readonly buffer velocityYout 
{   
    float vyout[];
    
};

layout (std430,binding = 10) readonly buffer Terrain 
{   
    float terr[];
    
};


uniform ivec2 size; 
uniform float dt; 

void main(){

    float GRAVITY = -9.81f;
    float C = dt*GRAVITY;
    ivec2 storePos = ivec2(gl_GlobalInvocationID.xy);
    int i = storePos.x;
    int j = storePos.y;
    int offset = (i + j*size.x);
    
    
    int ipos= clamp(i+1,0,size.x-1);
    int jpos = clamp(j+1,0,size.y-1);
    int imin = clamp(i-1,0,size.x-1);
    int jmin = clamp(j-1,0,size.y-1);
    
        //Coordinate system HERE! <  is to the right and up.

        int offsetright = ipos+j*size.x;
        int offsetleft = imin+j*size.x;
        int offsetup = i+jpos*size.x;
        int offsetdown = i+jmin*size.x;
        int offsettopright = ipos+jpos*size.x;
        int sampX,sampY;
    
    
    float ourWater = water0[offset];
    float ourTot = ourWater+terr[offset];
    
    if(i > 1  && i < size.x-1 && j < size.y-1) {
        float neighWater = water0[offsetleft];
        float neighTot = neighWater + terr[offsetleft];
        /* 
        float change = clamp(ourTot - neighTot,-ourWater/2.0f,neighWater/.0f);
        
        */
        
        float change = ourTot-neighTot;
        //vxin[offset] = clamp((vxout[offset] + C*change),-10.0f,10.0f);
        vxin[offset] = vxout[offset] + C*change;
        
    }
    if(j > 1  && i < size.x-1 && j < size.y-1) {
    
        float neighWater = water0[offsetdown];
        float neighTot = neighWater +terr[offsetdown];
        /* So this ensures that the velocities do not exceed too large values and tries to compensate for topology
        float change = clamp(ourTot-neighTot,-ourWater,neighWater);
                
        */
            
        float change = ourTot-neighTot;
        //vyin[offset] = clamp((vyout[offset] + C*change),-10.0f,10.0f);
        vyin[offset] = vyout[offset] + C*change;
    }
    
    if(i == 0 || i ==size.x -1){
        vyin[offset] = 0.0f;
    }
    if(j == 0 || j ==size.y -1){
        vxin[offset] = 0.0f;
    }
    
    
    
}