OpenGL HeightMap with vertex shader and QGLShaderProgram

Question

I want to render a terrain and apply colors depending on height.
I'm writing a Qt project, so use QGlShaderProgram.

My terrain grid is from (0,0,0) to (1000,0,1000) and vertices are placed every 100 length units. I wanted to transfer the data to the shader using an uniform array.

I still have problems sending data to the shader.

call from C++/Qt:

QGLShaderProgram  mShader;
QVector< GLfloat> mHeightMap (10*10, some_data);
GLfloat           mXStepSize = 100;
GLfloat           mZStepSize = 100;
// ..
mShader.link();
mShader.bind();
mShader.setUniformValueArray( "heights",
                               &(mHeightMap[0]),       // one line after another
                               mHeightMap.size(), 1 );
mShader.setUniformValue( "x_res", (GLint) mXStepSize);
mShader.setUniformValue( "z_res", (GLint) mZStepSize);

shader source:

uniform sampler2D heights;
uniform int       x_res;
uniform int       z_res;
void main(void)
{
       vec4 tmp         = gl_Vertex;
       vec4 h;
       float x_coord    = gl_Vertex[0] * 0.001;
       float z_coord    = gl_Vertex[2] * 0.001;

       // interprete as 2D:
       int element      = int( (x_coord + float(x_res)*z_coord) );

       h                = texture2D( heights, vec2(x_coord, z_coord));
       gl_FrontColor    = gl_Color;
       gl_FrontColor[1] = h[ element];     // set color by height
       tmp.y            = h[ element];     // write height to grid
       gl_Position      = gl_ModelViewProjectionMatrix * tmp;
}

Where is my mistake?
How should I load the data to the shader and then access it there?

Answer 1

You want to pass it as a texture, you must first convert your array map (mHeightMap) in a opengl texture using glTexImage2D. look at this , it might be what your looking for: https://gamedev.stackexchange.com/questions/45188/how-can-i-pass-an-array-of-floats-to-the-fragment-shader-using-textures

Edit: You might want to tweak some of it, but it's the idea:

//Create texture: 
glint texture;
glActiveTexture(GL_TEXTURE0);
glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);  
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);  
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);  
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);  
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);  
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, Width, Height, 0, GL_RGBA,
GL_UNSIGNED_BYTE, &(mHeightMap.constData()[data_start]));

//pass it to shader
glint uniformId = glGetUniformid(shader, "height");
glActiveTexture(GL_TEXTURE0);   
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, texture);  
glUniform1i(uniformId, 0); // 0 is the texture number

Answer 2

(the code seems to work now)

I figured most of it out, with the help of izissise. I used GL_TEXTURE_RECTANGLE instead of GL_TEXTURE_2D.
Still it uses only the red channel (this might be optimized).

this is my Initialization :

QGLShaderProgram    mShader;
QVector< GLfloat> mHeightMap (width * height * state_count, 
                              some_data);
mShader.link();

// init texture
glActiveTexture(GL_TEXTURE0);
glGenTextures(1, &mShaderTexture);
glBindTexture(GL_TEXTURE_RECTANGLE, mShaderTexture);

and sending data to shader (this may be repeated as often as wanted):

mShader.bind();
// ..
glTexImage2D(GL_TEXTURE_RECTANGLE, 0, GL_RED,
             width, depth, 0,
             GL_RED, GL_FLOAT,
             &(mHeightMap.constData()[mHeightMapPos])); // set portion of vector as array to texture / sampler
glActiveTexture(GL_TEXTURE0);
glEnable(GL_TEXTURE_RECTANGLE);
glBindTexture(GL_TEXTURE_RECTANGLE, mShaderTexture);
mShader.setUniformValue( "max_height",  (GLfloat) (250.0) );
mShader.setUniformValue( "x_steps",     (GLint) width);
mShader.setUniformValue( "z_steps",     (GLint) height);

// ..
mShader.release();

as well as the shader source :

uniform int     x_steps;
uniform int     z_steps;
uniform sampler2DRect heights;
uniform float   max_height;

void main(void)
{
    vec4 tmp         = gl_Vertex;
    vec4 h;

    float x_coord    = gl_Vertex[0] * 0.001 * float(x_steps-1);
    float z_coord    = gl_Vertex[2] * 0.001 * float(z_steps-1);
    h                = texture2DRect( heights, ivec2(int(x_coord), int(z_coord)) );
    tmp.y            = max_height * (h.r);

    gl_FrontColor    = gl_Color;
    gl_FrontColor[1] = h.r;

    gl_Position      = gl_ModelViewProjectionMatrix * tmp;
}