What is the easiest way to draw line using OpenGL-ES (android)

Question

If I have custom renderer in opengl-es prepared:

public void onDrawFrame(GL10 gl) {     gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);     // here i want to draw line from [0, 0, 0] to [1, 0, 0] } 

What is the easiest and shortest way to draw line?

In ordinary OpenGL it is:

glBegin(GL_LINES);     glVertex3f(0, 0, 0);     glVertex3f(1, 0, 0); glEnd(); 

But how can i get the same effect with OpenGL ES?

Answer 1

I am new to new to OpenGL ES 2.0 but I created a line class.

public class Line {     private FloatBuffer VertexBuffer;      private final String VertexShaderCode =         // This matrix member variable provides a hook to manipulate         // the coordinates of the objects that use this vertex shader         "uniform mat4 uMVPMatrix;" +          "attribute vec4 vPosition;" +         "void main() {" +         // the matrix must be included as a modifier of gl_Position         "  gl_Position = uMVPMatrix * vPosition;" +         "}";      private final String FragmentShaderCode =         "precision mediump float;" +         "uniform vec4 vColor;" +         "void main() {" +         "  gl_FragColor = vColor;" +         "}";      protected int GlProgram;     protected int PositionHandle;     protected int ColorHandle;     protected int MVPMatrixHandle;      // number of coordinates per vertex in this array     static final int COORDS_PER_VERTEX = 3;     static float LineCoords[] = {         0.0f, 0.0f, 0.0f,         1.0f, 0.0f, 0.0f     };      private final int VertexCount = LineCoords.length / COORDS_PER_VERTEX;     private final int VertexStride = COORDS_PER_VERTEX * 4; // 4 bytes per vertex      // Set color with red, green, blue and alpha (opacity) values     float color[] = { 0.0f, 0.0f, 0.0f, 1.0f };      public Line() {         // initialize vertex byte buffer for shape coordinates         ByteBuffer bb = ByteBuffer.allocateDirect(             // (number of coordinate values * 4 bytes per float)             LineCoords.length * 4);         // use the device hardware's native byte order         bb.order(ByteOrder.nativeOrder());          // create a floating point buffer from the ByteBuffer         VertexBuffer = bb.asFloatBuffer();         // add the coordinates to the FloatBuffer         VertexBuffer.put(LineCoords);         // set the buffer to read the first coordinate         VertexBuffer.position(0);          int vertexShader = ArRenderer.loadShader(GLES20.GL_VERTEX_SHADER, VertexShaderCode);         int fragmentShader = ArRenderer.loadShader(GLES20.GL_FRAGMENT_SHADER, FragmentShaderCode);          GlProgram = GLES20.glCreateProgram();             // create empty OpenGL ES Program         GLES20.glAttachShader(GlProgram, vertexShader);   // add the vertex shader to program         GLES20.glAttachShader(GlProgram, fragmentShader); // add the fragment shader to program         GLES20.glLinkProgram(GlProgram);                  // creates OpenGL ES program executables     }      public void SetVerts(float v0, float v1, float v2, float v3, float v4, float v5) {         LineCoords[0] = v0;         LineCoords[1] = v1;         LineCoords[2] = v2;         LineCoords[3] = v3;         LineCoords[4] = v4;         LineCoords[5] = v5;          VertexBuffer.put(LineCoords);         // set the buffer to read the first coordinate         VertexBuffer.position(0);     }      public void SetColor(float red, float green, float blue, float alpha) {         color[0] = red;         color[1] = green;         color[2] = blue;         color[3] = alpha;     }      public void draw(float[] mvpMatrix) {         // Add program to OpenGL ES environment         GLES20.glUseProgram(GlProgram);          // get handle to vertex shader's vPosition member         PositionHandle = GLES20.glGetAttribLocation(GlProgram, "vPosition");          // Enable a handle to the triangle vertices         GLES20.glEnableVertexAttribArray(PositionHandle);          // Prepare the triangle coordinate data         GLES20.glVertexAttribPointer(PositionHandle, COORDS_PER_VERTEX,                                  GLES20.GL_FLOAT, false,                                  VertexStride, VertexBuffer);          // get handle to fragment shader's vColor member         ColorHandle = GLES20.glGetUniformLocation(GlProgram, "vColor");          // Set color for drawing the triangle         GLES20.glUniform4fv(ColorHandle, 1, color, 0);          // get handle to shape's transformation matrix         MVPMatrixHandle = GLES20.glGetUniformLocation(GlProgram, "uMVPMatrix");         ArRenderer.checkGlError("glGetUniformLocation");          // Apply the projection and view transformation         GLES20.glUniformMatrix4fv(MVPMatrixHandle, 1, false, mvpMatrix, 0);         ArRenderer.checkGlError("glUniformMatrix4fv");          // Draw the triangle         GLES20.glDrawArrays(GLES20.GL_LINES, 0, VertexCount);          // Disable vertex array         GLES20.glDisableVertexAttribArray(PositionHandle);     }  } 

And then in my Render class I create my line objects and to a container so the get draw in the by iterating over the items and calling the Line.draw method in onDrawFrame.

Here are some lines I create to make a horizon:

    Line eastHorz = new Line();     eastHorz.SetVerts(10f, 10f, 0f, 10f, -10f, 0f);     eastHorz.SetColor(.8f, .8f, 0f, 1.0f);     Line northHorz = new Line();     northHorz.SetVerts(-10f, 10f, 0f, 10f, 10f, 0f);     northHorz.SetColor(0.8f, 0.8f, 0f, 1.0f);     Line westHorz = new Line();     westHorz.SetVerts(-10f, -10f, 0f, -10f, 10f, 0f);     westHorz.SetColor(0.8f, 0.8f, 0f, 1.0f);     Line southHorz = new Line();     southHorz.SetVerts(-10f, -10f, 0f, 10f, -10f, 0f);     southHorz.SetColor(0.8f, 0.8f, 0f, 1.0f);     Lines.add(eastHorz);     Lines.add(northHorz);     Lines.add(westHorz);     Lines.add(southHorz);