i am trying to implement a 3d aplication for android and i am having trouble when drawing 3d objects like a cone for example. The problem is that i cant notice the transitions between the different faces, all of them are draw with the same color. I think i need to add shading to the polygons but i cant find any tutorial showing me how do i do that. this is the code i am using to draw a cone.
public class Cone{
float baseSize = 0f;
float height = 0f;
protected final float[] mTransformMatrix = new float[16];
private FloatBuffer vertexBuffer;
private final int mProgram;
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
// Note that the uMVPMatrix factor *must be first* in order
// for the matrix multiplication product to be correct.
" gl_Position = uMVPMatrix * vPosition;" +
"}";
// Use to access and set the view transformation
private int mMVPMatrixHandle;
private final String fragmentShaderCode =
"precision mediump float;" +
"uniform vec4 vColor;" +
"void main() {" +
" gl_FragColor = vColor;" +
"}";
// number of coordinates per vertex in this array
static final int COORDS_PER_VERTEX = 3;
static float topCoords[] = new float[30];
static float baseCoords[] = new float[30];
static float lineCoords[] = new float[96];
// Set color with red, green, blue and alpha (opacity) values
float color[] = { 1f, 0f, 0f, 1.0f };
float linecolor[] = { 1f, 1f, 1f, 1.0f };
public Cone(float baseSize , float height) {
this.baseSize = baseSize;
this.height = height;
float ang = (float) ((2*Math.PI) / 8);
Matrix.setIdentityM(mTransformMatrix, 0);
// initialize vertex byte buffer for shape coordinates
ByteBuffer bb = ByteBuffer.allocateDirect(
// (number of coordinate values * 4 bytes per float)
(topCoords.length * 2 + 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
topCoords[0] = 0;
topCoords[1] = height;
topCoords[2] = 0;
baseCoords[0]= 0;
baseCoords[1]= 0;
baseCoords[2]= 0;
for(int i=1; i < 10;i++) {
topCoords[i*3] = this.baseSize * (float) Math.cos(i*ang);
topCoords[i*3 + 1] = 0;
topCoords[i*3 + 2] = this.baseSize * (float) Math.sin(i*ang);
baseCoords[i*3] = this.baseSize * (float) Math.cos(i*ang);
baseCoords[i*3 + 1] = 0;
baseCoords[i*3 + 2] = this.baseSize * (float) Math.sin(i*ang);
}
for (int i = 0 ; i < 8 ; i ++) {
lineCoords[i*6] = 0;
lineCoords[i*6 + 1] = height;
lineCoords[i*6 + 2] = 0;
lineCoords[i*6 + 3] = this.baseSize *(float) Math.cos((i+1)*ang);
lineCoords[i*6 + 4] = 0;
lineCoords[i*6 + 5] = this.baseSize * (float) Math.sin((i+1)*ang);
}
int j = 0;
for (int i = 8 ; i < 16 ; i++){
lineCoords[i*6] = this.baseSize *(float) Math.cos((j+1)*ang);
lineCoords[i*6 + 1] = 0;
lineCoords[i*6 + 2] = this.baseSize * (float) Math.sin((j+1)*ang);
lineCoords[i*6 + 3] = this.baseSize *(float) Math.cos((j+2)*ang);
lineCoords[i*6 + 4] = 0;
lineCoords[i*6 + 5] = this.baseSize * (float) Math.sin((j+2)*ang);
j++;
}
vertexBuffer.put(topCoords);
vertexBuffer.put(baseCoords);
vertexBuffer.put(lineCoords);
// set the buffer to read the first coordinate
vertexBuffer.position(0);
int vertexShader = MyGLRenderer.loadShader(GLES20.GL_VERTEX_SHADER,
vertexShaderCode);
int fragmentShader = MyGLRenderer.loadShader(GLES20.GL_FRAGMENT_SHADER,
fragmentShaderCode);
// create empty OpenGL ES Program
mProgram = GLES20.glCreateProgram();
// add the vertex shader to program
GLES20.glAttachShader(mProgram, vertexShader);
// add the fragment shader to program
GLES20.glAttachShader(mProgram, fragmentShader);
// creates OpenGL ES program executables
GLES20.glLinkProgram(mProgram);
}
private int mPositionHandle;
private int mColorHandle;
private final int topVertexCount = topCoords.length / COORDS_PER_VERTEX;
private final int lineVertexCount = lineCoords.length / COORDS_PER_VERTEX;
private final int vertexStride = COORDS_PER_VERTEX * 4; // 4 bytes per vertex
public void draw(float[] mvpMatrix) {
// Add program to OpenGL ES environment
GLES20.glUseProgram(mProgram);
// get handle to vertex shader's vPosition member
mPositionHandle = GLES20.glGetAttribLocation(mProgram, "vPosition");
// Enable a handle to the triangle vertices
GLES20.glEnableVertexAttribArray(mPositionHandle);
// Prepare the triangle coordinate data
GLES20.glVertexAttribPointer(mPositionHandle, COORDS_PER_VERTEX,
GLES20.GL_FLOAT, false,
vertexStride, vertexBuffer);
// get handle to fragment shader's vColor member
mColorHandle = GLES20.glGetUniformLocation(mProgram, "vColor");
// Set color for drawing the cone
GLES20.glUniform4fv(mColorHandle, 1, color, 0);
// get handle to shape's transformation matrix
mMVPMatrixHandle = GLES20.glGetUniformLocation(mProgram, "uMVPMatrix");
// Pass the projection and view transformation to the shader
GLES20.glUniformMatrix4fv(mMVPMatrixHandle, 1, false, mvpMatrix, 0);
// Draw the cone
GLES20.glDrawArrays(GLES20.GL_TRIANGLE_FAN, 0, topVertexCount);
//Draw base
GLES20.glDrawArrays(GLES20.GL_TRIANGLE_FAN, topVertexCount, topVertexCount);
//Draw cone lines
GLES20.glUniform4fv(mColorHandle, 1, linecolor, 0);
GLES20.glDrawArrays(GLES20.GL_LINES, topVertexCount*2, lineVertexCount);
// Disable vertex array
GLES20.glDisableVertexAttribArray(mPositionHandle);
}
}
Thanks for the help
