extend CustomOverlay example to draw a triangle

src/org/oscim/renderer/overlays/CustomOverlay.java

@@ -14,28 +14,128 @@
  */
 package org.oscim.renderer.overlays;
 
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import java.nio.FloatBuffer;
+
 import org.oscim.core.MapPosition;
+import org.oscim.renderer.GLState;
+import org.oscim.utils.GlUtils;
 import org.oscim.view.MapView;
 
+import android.opengl.GLES20;
+import android.opengl.Matrix;
+
+// http://safari.informit.com/9780321563835
+// http://www.opengles-book.com
+
 public class CustomOverlay extends RenderOverlay {
 
+	private int mProgramObject;
+	private int hVertexPosition;
+	private int hMatrixPosition;
+
+	private FloatBuffer mVertices;
+	private final float[] mVerticesData = {
+			0, 200, 0,
+			-200, -200, 0,
+			200, -200, 0
+	};
+	private boolean mInitialized;
+
 	public CustomOverlay(MapView mapView) {
 		super(mapView);
 	}
 
+	// ---------- everything below runs in GLRender Thread ----------
 	@Override
 	public void update(MapPosition curPos, boolean positionChanged, boolean tilesChanged) {
-		// tell GLRender to call 'compile'
-		newData = true;
+		if (!mInitialized) {
+			if (!init())
+				return;
+
+			// tell GLRender to call 'compile' when data has changed
+			newData = true;
+
+			mInitialized = true;
+		}
 	}
 
 	@Override
 	public void compile() {
+		// modify mVerticesData and put in FloatBuffer
+
+		mVertices.clear();
+		mVertices.put(mVerticesData);
+		mVertices.flip();
+
+		newData = false;
+
 		// tell GLRender to call 'render'
 		isReady = true;
 	}
 
 	@Override
-	public void render(MapPosition pos, float[] mv, float[] proj) {
+	public void render(MapPosition pos, float[] tmp, float[] proj) {
+
+		// Use the program object
+		GLState.useProgram(mProgramObject);
+
+		GLState.blend(true);
+		GLState.test(false, false);
+
+		// unbind previously bound VBOs
+		GLES20.glBindBuffer(GLES20.GL_ARRAY_BUFFER, 0);
+
+		// Load the vertex data
+		mVertices.position(0);
+		GLES20.glVertexAttribPointer(hVertexPosition, 3, GLES20.GL_FLOAT, false, 0, mVertices);
+		GLState.enableVertexArrays(hVertexPosition, -1);
+
+		// apply view and projection matrices
+		Matrix.multiplyMM(tmp, 0, proj, 0, pos.viewMatrix, 0);
+		GLES20.glUniformMatrix4fv(hMatrixPosition, 1, false, tmp, 0);
+
+		// Draw the triangle
+		GLES20.glDrawArrays(GLES20.GL_TRIANGLES, 0, 3);
+
+		GlUtils.checkGlError("...");
 	}
+
+	private boolean init() {
+		// Load the vertex/fragment shaders
+		int programObject = GlUtils.createProgram(vShaderStr, fShaderStr);
+
+		if (programObject == 0)
+			return false;
+
+		// Handle for vertex position in shader
+		hVertexPosition = GLES20.glGetAttribLocation(programObject, "a_pos");
+		hMatrixPosition = GLES20.glGetUniformLocation(programObject, "u_mvp");
+
+		// Store the program object
+		mProgramObject = programObject;
+
+		mVertices = ByteBuffer.allocateDirect(mVerticesData.length * 4)
+				.order(ByteOrder.nativeOrder()).asFloatBuffer();
+
+		return true;
+	}
+
+	private final static String vShaderStr =
+			"precision mediump float;"
+					+ "uniform mat4 u_mvp;"
+					+ "attribute vec4 a_pos;"
+					+ "void main()"
+					+ "{"
+					+ "   gl_Position = u_mvp * a_pos;"
+					+ "}";
+
+	private final static String fShaderStr =
+			"precision mediump float;"
+					+ "void main()"
+					+ "{"
+					+ "  gl_FragColor = vec4 ( 0.0, 0.0, 0.0, 0.7 );"
+					+ "}";
+
 }