How to draw basic circle in OpenGL ES 2.0 Android

Question

I\'m new in OpenGL ES 2, and I have read many topics about how to draw a circle in OpenGL ES 2 on Android. Based on Drawing Shapes and this code found on gamedev.net, I can

Answer 1

If you want to create geometry for the circle, do something like this:

int vertexCount = 30;
float radius = 1.0f;
float center_x = 0.0f;
float center_y = 0.0f;

// Create a buffer for vertex data
float buffer[] = new float[vertexCount*2]; // (x,y) for each vertex
int idx = 0;

// Center vertex for triangle fan
buffer[idx++] = center_x;
buffer[idx++] = center_y;

// Outer vertices of the circle
int outerVertexCount = vertexCount-1;

for (int i = 0; i < outerVertexCount; ++i){
    float percent = (i / (float) (outerVertexCount-1));
    float rad = percent * 2*Math.PI;

    //Vertex position
    float outer_x = center_x + radius * cos(rad);
    float outer_y = center_y + radius * sin(rad);

    buffer[idx++] = outer_x;
    buffer[idx++] = outer_y;
}

//Create VBO from buffer with glBufferData()

Then you can draw using glDrawArrays() either as:

• GL_LINE_LOOP(contour only) or
• GL_TRIANGLE_FAN(filled shape)

.

// Draw circle contours (skip center vertex at start of the buffer)
glDrawArrays(GL_LINE_LOOP, 2, outerVertexCount);

// Draw circle as a filled shape
glDrawArrays(GL_TRIANGLE_FAN, 0, vertexCount);