How to modify algorithm to return a triangle with different colors of vertices?

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How to modify algorithm to return a triangle with different colors of vertices?

I have fragment and vertex, and I am not able to call in the java code, to compile a triangle, with each vertex defining a color.

package Projeto_2;

import com.jogamp.opengl.*;
import com.jogamp.newt.opengl.GLWindow;
import com.jogamp.opengl.util.Animator;


* <BR>
* Java implementation of example (listing 2.8 and 2.9) of the OpenGL  SuperBible 6th Edition.
 * Not exactly the same but an adaptation.

public final class Projeto_2 implements GLEventListener {

private GL4 gl;

private static int width=600;
private static int height=600;

private int shaderProgram;
private int vertShader;
private int fragShader;

private int[] vao;

public static void main(String[] s) {

    // This demo is based on the GL4 GLProfile
    GLCapabilities caps = new GLCapabilities(GLProfile.get(GLProfile.GL4));

    // The demo uses the NEWT (Native Windowing Toolkit) Programming Library
    GLWindow glWindow = GLWindow.create(caps);

    // Setup the GLWindow
    glWindow.setTitle("Single Triangle - JOGL");

    // Finally we connect the GLEventListener application code to the GLWindow.
    // GLWindow will call the GLEventListener init, reshape, display and dispose functions when needed.
    glWindow.addGLEventListener(new Projeto_2());
    Animator animator = new Animator();

public void init(GLAutoDrawable drawable) {

    gl = drawable.getGL().getGL4();

    // Create GPU shader handles
    vertShader = loadShader(GL4.GL_VERTEX_SHADER, "./src/shader.vert");
    fragShader = loadShader(GL4.GL_FRAGMENT_SHADER, "./src/shader.frag");
    //Each shaderProgram must have one vertex shader and one fragment shader.
    shaderProgram = gl.glCreateProgram();
    gl.glAttachShader(shaderProgram, vertShader);
    gl.glAttachShader(shaderProgram, fragShader);      

    //gl.glBindAttribLocation(shaderProgram, 0, "attribute_Position"); /////////////////////////////
   // gl.glBindAttribLocation(shaderProgram, 1, "attribute_Color"); ////////////////////////////

    // Check link status.
    int[] linked = new int[1];
    gl.glGetProgramiv(shaderProgram, GL4.GL_LINK_STATUS, linked, 0);
    if(linked[0]!=0){System.out.println("Shaders succesfully linked");}
    else {
        int[] logLength = new int[1];
        gl.glGetProgramiv(shaderProgram, GL4.GL_INFO_LOG_LENGTH, logLength, 0);

        byte[] log = new byte[logLength[0]];
        gl.glGetProgramInfoLog(shaderProgram, logLength[0], (int[])null, 0, log, 0);

        System.err.println("Error linking shaders: " + new String(log));


    vao = new int[1];
    gl.glGenVertexArrays(1, vao, 0);


public void reshape(GLAutoDrawable drawable, int x, int y, int z, int h) {
    System.out.println("reshape - Window resized to width=" + z + " height=" + h);
    width = z;
    height = h;

    // Optional: Set viewport
    // Render to a square at the center of the window.
    gl.glViewport((width-height)/2, 0, height, height);

public void display(GLAutoDrawable drawable) {
    float[] bg = {0.0f, 0.0f, 0.0f, 1.0f};
    gl.glClearBufferfv(GL4.GL_COLOR, 0, bg, 0);

    gl.glDrawArrays(GL4.GL_TRIANGLES, 0, 3);

public void dispose(GLAutoDrawable drawable) {
    System.out.println("cleanup, remember to release shaders");
    gl.glDetachShader(shaderProgram, vertShader);
    gl.glDetachShader(shaderProgram, fragShader);

public int loadShader(int type, String filename ) {
    int shader;

    // Create GPU shader handle
    shader = gl.glCreateShader(type);

    // Read shader file
    String[] vlines = new String[1];
    vlines[0] = "";
    String line;

        BufferedReader reader = new BufferedReader(new FileReader(filename));
        while((line = reader.readLine()) != null) {
            vlines[0] += line + "\n";  // insert a newline character after each line
    } catch (Exception e) {
        System.err.println("Fail reading shader file");

    gl.glShaderSource(shader, vlines.length, vlines, null);

    // Compile shader

    // Check compile status.
    int[] compiled = new int[1];
    gl.glGetShaderiv(shader, GL4.GL_COMPILE_STATUS, compiled, 0);
    if(compiled[0]!=0){System.out.println("Shader succesfully compiled");}
    else {
        int[] logLength = new int[1];
        gl.glGetShaderiv(shader, GL4.GL_INFO_LOG_LENGTH, logLength, 0);

        byte[] log = new byte[logLength[0]];
        gl.glGetShaderInfoLog(shader, logLength[0], (int[])null, 0, log, 0);

        System.err.println("Error compiling the shader: " + new String(log));

    return shader;
I do not know what function to call the two shaders, to generate this triangle with three vertices and each vertex defining the colors red, blue and green.


 #version 400 core

 in vec4 varying_Color; // incoming varying data to the
                   // fragment shader
                   // sent from the vertex shader

 void main (void) {
 gl_FragColor = varying_Color;

#version 400 core

in vec4 attribute_Position; // vertex shader
in vec4 attribute_Color; // attributes

out vec4 varying_Color; // Outgoing varying data
                    // sent to the fragment shader
void main (void) {
varying_Color = attribute_Color;
gl_Position = attribute_Position;

Remembering that I can not modify the shaders, just the java code! How to proceed???
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Re: How to modify algorithm to return a triangle with different colors of vertices?

This post was updated on .
Easy, you need to provide data for the color attribute in the buffer object you provide.

But the code you provided it's incomplete, you need buffer(s) and vertex array(s).

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Re: How to modify algorithm to return a triangle with different colors of vertices?

What buffer (s) and arrays will I use? Sorry for the somewhat obvious questions I'm learning to program and do not understand some concepts yet.
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Re: How to modify algorithm to return a triangle with different colors of vertices?

You need to put your vertex positions and colors into a buffer and upload it to the gpu, like here.

You also need to say to OpenGL how it should read your data, like here.

And then your vertex shader will fetch attribute_Position and attirbute_Color accordingly.

If completely newbie, consider following a tutorial, like this one.