Drawing triangle using OpenGl not showing up?
I am trying to make my first application. based on OpenGl I am trying to draw a triangle and wHEN
USE OF THE APP. it just displays a black screen with no triangle.
1-I don't know where is my mistake? 2-is there a good book / tutorials for newbies to open Android?
Triangle class:
public class Triangle {
private FloatBuffer vertxBuffer;
protected static byte indices[] = {
//Face definition:
0,1,3, //lower-right triangle of the face is drawn with vertices vertices[0]->vertices[1]->vertices[3] (->vertices[0])
0,3,2 //upper-right triangle of the face is drawn with vertices vertices[0]->vertices[3]->vertices[2] (->vertices[0])
};
public float vertices[] = {
-0.5f, -0.5f, 0.0f,
0.5f, -0.5f, 0.0f,
0.0f, 0.5f, 0.0f
};
public Triangle() {
// float has 4 bytes, so we allocate for each coordinate 4 bytes.
//what is the difference between ByteBuffer.allocateDirect AND ByteBuffer.allocate???
ByteBuffer vertexByteBuffer = ByteBuffer.allocateDirect(vertices.length * 4);
vertexByteBuffer.order(ByteOrder.nativeOrder());
// allocate the memory from the byte buffer
vertxBuffer = vertexByteBuffer.asFloatBuffer();
//fill the vertex buffer with the vertices
vertxBuffer.put(vertices);
// set the cursor position to the beginning of the buffer
vertexByteBuffer.position(0);
}
protected static ByteBuffer indexBuffer;
static {
indexBuffer = ByteBuffer.allocateDirect(indices.length);
indexBuffer.put(indices);
indexBuffer.position(0);
}
public void draw(GL10 gl) {
// Because we store the Triangle vertices " Coordinates " in a FloatBuffer
// we need to enable OpenGL to read from it.
gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
//set the color for the Triangle (r, g, b, alpha) alpha is between 0-1
gl.glColor4f(2.0f, 1.0f, 0.0f, 0.5f);
// point to our vertex buffer to extract the vertices from it.
//(numberOfVertices, Which type of data the buffer Holds, offset, our Buffer containing the Vertices)
gl.glVertexPointer(3, GL10.GL_FLOAT, 0, vertxBuffer);
//draw the vertices as triangle strip
gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 0, vertices.length/3 );
gl.glDrawElements(gl.GL_TRIANGLES, indices.length, gl.GL_UNSIGNED_BYTE, indexBuffer);
//disable the client state before leaving
gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);
}
}
GLRenderer class:
public class GLRenderer implements Renderer{
private Triangle triangle;
public GLRenderer() {
this.triangle = new Triangle();
}
@Override
public void onDrawFrame(GL10 gl) {
// TODO Auto-generated method stub
// clear screen and depth buffer
gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);
// reset the mode view matrix
gl.glLoadIdentity();
// Drawing
gl.glTranslatef(0.0f, 0.0f, -5.0f);
triangle.draw(gl);
}
@Override
public void onSurfaceChanged(GL10 gl, int width, int height) {
// TODO Auto-generated method stub
if (height == 0) {
height = 1;
}
//Reset the current View Port
gl.glViewport(0, 0, width, height);
//Select the Projection Matrix
gl.glMatrixMode(GL10.GL_PROJECTION);
// Reset the Projection Matrix
gl.glLoadIdentity();
// calculate the aspect ratio of the window
GLU.gluPerspective(gl, 45.0f, (float) width/(float) height, 0.1f , 100.0f);
gl.glMatrixMode(GL10.GL_MODELVIEW);
gl.glLoadIdentity();
}
@Override
public void onSurfaceCreated(GL10 gl, EGLConfig config) {
// TODO Auto-generated method stub
gl.glClearColor(0, 0, 0, 1.0f);
gl.glClearDepthf(1.0f);
gl.glEnable(GL10.GL_DEPTH_TEST);
gl.glDepthFunc(GL10.GL_LEQUAL);
gl.glHint(GL10.GL_PERSPECTIVE_CORRECTION_HINT, GL10.GL_NICEST);
gl.glShadeModel(GL10.GL_SMOOTH);
gl.glDisable(GL10.GL_DITHER);
}
}
OpenGlRenderActivity class:
public class OpenGLRenderActivity extends Activity {
/** Called when the activity is first created. */
private GLSurfaceView gLSurfaceView;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
//requestWindowFeature(Window.FEATURE_NO_TITLE);
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
WindowManager.LayoutParams.FLAG_FULLSCREEN);
gLSurfaceView = new GLSurfaceView(this);
gLSurfaceView.setRenderer(new GLRenderer());
setContentView(gLSurfaceView);
}
@Override
protected void onResume() {
super.onResume();
gLSurfaceView.onResume();
}
@Override
protected void onPause() {
super.onPause();
gLSurfaceView.onPause();
}
}
I think you need to declare indices for your vertex (to make up the lines and edges):
protected static byte indices[] = {
//Face definition:
0,1,3, //lower-right triangle of the face is drawn with vertices vertices[0]->vertices[1]->vertices[3] (->vertices[0])
0,3,2 //upper-right triangle of the face is drawn with vertices vertices[0]->vertices[3]->vertices[2] (->vertices[0])
};
protected static ByteBuffer indexBuffer;
static {
indexBuffer = ByteBuffer.allocateDirect(indices.length);
indexBuffer.put(indices);
indexBuffer.position(0);
}
then pass those indices to your draw call:
(replace
gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 0, vertices.length/3 );
from
gl.glDrawElements(GL.GL_TRIANGLES, indices.length, GL.GL_UNSIGNED_BYTE, indexBuffer)
;
)
As far as tutorials go, you have great Android versions from Nehe:
http://insanitydesign.com/wp/projects/nehe-android-ports/
This is more code than textual explanations, but it gets you going very slowly and the code will work well. Actually I think one of the first tutrials just shows how to draw a triangle in the same way you are trying here.
Your triangles are clipped near the clipping plane. Try moving it between the near and far gluPerspective values.
This Android tutorial talks about the requirement of a vertex shader, a fragment shader and a program. I may have missed this, but I don't see anything like this in your code. In my case, the fix for the invisible triangle was to capture type-o in my fragment file.