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# OpenGL How to store an array into a texture and sampler the texture in vertex shader correctly?

## 1 post in this topic

I'm a new learner about OpenGL and GLSL. I'm coding a program in which i wanna store a group of datas in a texture and get the data by sampling the texture in vertex shader. Then i want to set the datas as the y coodinates of terrain positions. But i get a trouble that it's failed and i can't get a correct value___all the y coodinates are 0.

The main code is below:

    GLuint  terrainShader;      // The perspective demonstration shader
GLint   locMVP,locTex;                 // The location of the uniform in vertex shader

GLuint  vao;                    // The VAO
GLuint  vertexBuffer;
GLuint elementBuffer;
GLuint vertexTexture;

const int n=127;
float verteces[n*n*2];// vertex array
GLuint vIndexFine[(n-1)*2*n];//index array
GLsizei countFine[n-1];
GLvoid* offsetFine[n-1];

float *data=new float[n*n];
GLT_ATTRIBUTE_VERTEX, "vVertex");

//creat a terrain with size of n*n
for(int i=0;i<n;i++)
{
int sum=i*n;
for(int j=0;j<n;j++)
{
verteces[(sum+j)*2]=float(j);
verteces[(sum+j)*2+1]=float(i);
}
}
//initialize the index array
for(int i=0;i<n-1;i++)
{
if(i==0) //the first line
{
for(int j=0;j<n;j++)
{
vIndexFine[2*j]=j;
vIndexFine[2*j+1]=j+n;
}
}
else
{ //if it's not the first line,then just add n to get the indexes of new line
for(int k=0;k<2*n;k++)
{
vIndexFine[i*2*n+k]=vIndexFine[(i-1)*2*n+k]+n;
}
}
}

glGenVertexArrays(1, &vao);
glBindVertexArray(vao);

glGenBuffers(1, &vertexBuffer);
glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(verteces), verteces, GL_STATIC_DRAW);
glVertexAttribPointer(GLT_ATTRIBUTE_VERTEX, 2, GL_FLOAT, GL_FALSE, 0, NULL);
glEnableVertexAttribArray(GLT_ATTRIBUTE_VERTEX);

glGenBuffers(1, &elementBuffer);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, elementBuffer);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(vIndexFine), vIndexFine, GL_STATIC_DRAW);
//initialize data array with random integers between 1 and 100
for(int i=0;i<n*n;i++)
data[i]=float(rand()%100)/100.0;

//creat a texture and store data
glGenTextures(1, &vertexTexture);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, vertexTexture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_R32F, n,n, 0,GL_RED, GL_FLOAT, data);

//compute every trianglestrip's indexcount and offset
int temp=n*2*sizeof(GLuint);
for(int i=0;i<n-1;i++)
{
offsetFine[i]=(void*)(temp*i);
countFine[i]=GLsizei(n*2);
}

glUniform1i(locTex, 0);

modelViewMatrix.PushMatrix(viewFrame);
modelViewMatrix.Translate(-n/2.0, -10.0f, -n/2.0);
glUniformMatrix4fv(locMVP, 1, GL_FALSE, transformPipeline.GetModelViewProjectionMatrix());
glMultiDrawElements(GL_TRIANGLE_STRIP,countFine,GL_UNSIGNED_INT, (const GLvoid**)offsetFine,n-1);
modelViewMatrix.PopMatrix();

    #version 410

uniform mat4 mvpMatrix;
uniform sampler2D vertexTexture;
in vec2 vVertex;

void main(void)
{
vec2 vTexCoords=vVertex/127.0;
float height = texture2DLod(vertexTexture, vTexCoords,0.0).x*100.0;
vec4 position=vec4(vVertex.x,height,vVertex.y,1.0);
gl_Position = mvpMatrix * position;
}

i think  the mistake must be the part of storing datas in application or the part of fetching datas from  the texture in vertex shader. can sombody point it out for me?
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the problem is solved at here.

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