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How to Read Data from a Compute Shader using a UBO?

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How to Read Data from a Compute Shader using a UBO?
« on: July 16, 2018, 06:14:49 »
I am trying to read a ton of floats from a compute shader into a buffer. I simply have no idea how to do this, and I have searched and tried to follow things such as tutorials and other forums. Sadly, I just don't understand how to read my data from my Compute Shader into a FloatBuffer.

Compute Shader:
Code: [Select]
#version 430

uniform vec3 startPos;
uniform int xSize;
uniform int ySize;
uniform int zSize;


layout(std430, binding = 1) buffer Vals
{
float vals[];

};


uniform Vals {
uniform float vals[];
};

layout(local_size_x = 1, local_size_y = 1, local_size_z = 1) in;

vec3 random3(vec3 c) {
float j = 4096.0*sin(dot(c,vec3(17.0, 59.4, 15.0)));
vec3 r;
r.z = fract(512.0*j);
j *= .125;
r.x = fract(512.0*j);
j *= .125;
r.y = fract(512.0*j);
return r-0.5;
}

/* skew constants for 3d simplex functions */
const float F3 =  0.3333333;
const float G3 =  0.1666667;

/* 3d simplex noise */
float simplex3d(vec3 p) {
/* 1. find current tetrahedron T and it's four vertices */
/* s, s+i1, s+i2, s+1.0 - absolute skewed (integer) coordinates of T vertices */
/* x, x1, x2, x3 - unskewed coordinates of p relative to each of T vertices*/

/* calculate s and x */
vec3 s = floor(p + dot(p, vec3(F3)));
vec3 x = p - s + dot(s, vec3(G3));

/* calculate i1 and i2 */
vec3 e = step(vec3(0.0), x - x.yzx);
vec3 i1 = e*(1.0 - e.zxy);
vec3 i2 = 1.0 - e.zxy*(1.0 - e);

/* x1, x2, x3 */
vec3 x1 = x - i1 + G3;
vec3 x2 = x - i2 + 2.0*G3;
vec3 x3 = x - 1.0 + 3.0*G3;

/* 2. find four surflets and store them in d */
vec4 w, d;

/* calculate surflet weights */
w.x = dot(x, x);
w.y = dot(x1, x1);
w.z = dot(x2, x2);
w.w = dot(x3, x3);

/* w fades from 0.6 at the center of the surflet to 0.0 at the margin */
w = max(0.6 - w, 0.0);

/* calculate surflet components */
d.x = dot(random3(s), x);
d.y = dot(random3(s + i1), x1);
d.z = dot(random3(s + i2), x2);
d.w = dot(random3(s + 1.0), x3);

/* multiply d by w^4 */
w *= w;
w *= w;
d *= w;

/* 3. return the sum of the four surflets */
return dot(d, vec4(52.0));
}


void main() {

vals[gl_GlobalInvocationID.x + gl_GlobalInvocationID.y * xSize + gl_GlobalInvocationID.z * xSize * ySize] = simplex3d(gl_GlobalInvocationID);


}


The Java Code:
Code: [Select]
package shaders;

import java.nio.ByteBuffer;
import java.nio.FloatBuffer;

import org.lwjgl.BufferUtils;
import org.lwjgl.opengl.GL15;
import org.lwjgl.opengl.GL20;
import org.lwjgl.opengl.GL30;
import org.lwjgl.opengl.GL31;
import org.lwjgl.opengl.GL33;
import org.lwjgl.opengl.GL42;
import org.lwjgl.opengl.GL43;





import math.Vector3f;

public class SimplexNoiseComputeShader extends ComputeShaderProgram {

private static final String shaderFile = "src/shaders/SimplexNoiseComputeShader.txt";

private int location_startPos;
private int location_xSize;
private int location_ySize;
private int location_zSize;


private boolean isDone = false;

public FloatBuffer vals;

private int xSize;
private int ySize;
private int zSize;


private int totalSize;

private int ubo;

public SimplexNoiseComputeShader(Vector3f startPos, int xSize, int ySize, int zSize) {
super(shaderFile);

this.xSize = xSize;
this.ySize = ySize;
this.zSize = zSize;

totalSize = xSize * ySize * zSize;


// TODO Auto-generated constructor stub
//Load the start position for our compute shader
location_startPos = super.getUniformLocation("startPos");

location_xSize = super.getUniformLocation("xSize");
location_ySize = super.getUniformLocation("ySize");
location_zSize = super.getUniformLocation("zSize");


super.loadVector3f(location_startPos, startPos);
super.loadInt(location_xSize, xSize);
super.loadInt(location_ySize, ySize);
super.loadInt(location_zSize, zSize);




//start the compute shader!
start();
run();



//ByteBuffer bb = GL30.glMapBufferRange(ssbo, 0, totalSize, GL15.GL_READ_ONLY);
//vals = bb.asFloatBuffer();


//clean up the compute shader
CleanUp();
isDone = true;


}

private void run() {
GL43.glDispatchCompute(xSize, ySize, zSize);
}





}