CODEWITHSUNDEEP
androidopengl-es
Caio Keto
Caio Keto

Reputation: 2209

Android - Why i'm getting fatal signal?

Im trying to display some points on the screen with opengl es. here is the code of ondraw:

gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);
gl.glLoadIdentity();
gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
gl.glColor4f(0, 255, 0, 0);     
gl.glVertexPointer(3, GL10.GL_FLOAT, 0, buffer);
gl.glDrawArrays(GL10.GL_POINTS, 0, points.length);
gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);

Can someone tell me what I'm doing wrong???

EDIT: the code to generate the buffer and points

    points = new float[12288];
    int pos = 0;
    for (float y = 0; y < 64; y++) {
        for (float x = 0; x < 64; x++) {
            points[pos++] = x/100;
            points[pos++] = y/100;
            points[pos++] = 0;
        }
    }

    ByteBuffer vertexByteBuffer = ByteBuffer.allocateDirect(points.length * 4);
    vertexByteBuffer.order(ByteOrder.nativeOrder());     
    // allocates the memory from the byte buffer
    buffer = vertexByteBuffer.asFloatBuffer();   
    // fill the vertexBuffer with the vertices
    buffer.put(points);  
    // set the cursor position to the beginning of the buffer
    buffer.position(0);

and the error at logcat:

04-17 06:38:11.296: A/libc(24276): Fatal signal 11 (SIGSEGV) at 0x41719000 (code=2)

This error happens at gl.glDrawArrays

Upvotes: 3

Views: 3780

Answers (2)

Tim
Tim

Reputation: 35923

I believe this is the problem:

gl.glDrawArrays(GL10.GL_POINTS, 0, points.length);

glDrawArrays takes the number of vertices that you want to draw. You are giving it the number of floats, which is 3x too big. Therefore opengl is actually attempting to read 12288 vertices = 36,xxx floats from your points array, which way exceeds the bounds of your array.

Upvotes: 2

Robert Massaioli
Robert Massaioli

Reputation: 13477

Problem: You have not called glBindBuffer but you then called glDrawArrays; this will cause a segfault.

I had the same problem when I tried to use an IBO buffer without first binding the buffer using the glBindBuffer command. For example, one of my draw functions looks like this:

GLES20.glBindBuffer(GLES20.GL_ARRAY_BUFFER, common.vbo);
GLES20.glBindBuffer(GLES20.GL_ELEMENT_ARRAY_BUFFER, common.ibo);

GLES20.glVertexAttribPointer(handleManager.switchPosition, 2, GLES20.GL_FLOAT, false, 0, 0);
GLES20.glEnableVertexAttribArray(handleManager.switchPosition);

GLES20.glDrawElements(GLES20.GL_TRIANGLES, common.iboPointCount, GLES20.GL_UNSIGNED_BYTE, 0);

GLES20.glDisableVertexAttribArray(handleManager.switchPosition);

GLES20.glBindBuffer(GLES20.GL_ARRAY_BUFFER, 0);
GLES20.glBindBuffer(GLES20.GL_ELEMENT_ARRAY_BUFFER, 0);

All of the glBindBuffer commands make it possible to operate on the attribute data that you are trying to get the shader to recognise.

Upvotes: 0

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