"I think I've found the problem . I was setting the positions of only 359 vertices out of 404 vertices (nr of subdivisions + 1 times 4) . It seems the rest of the vertices were stuck at 0,0 on the screen . Allowing both FOR statements to cycle up to 404 seems to solve the problem"
Trying to create a circle with VBO's - LWJGL
Question
Im trying to create a circle in LWJGL , using VBO's and VAO , and move it using an offset , but it seems one vertex is stuck in the center of the screen . I can't figure out how to move it to the new location . Any help is appreciated , thanks !
P.S : I have already tried debugging the program , but I can't locate the faulty vertex in my array
import java.nio.FloatBuffer;
import org.lwjgl.BufferUtils;
import org.lwjgl.LWJGLException;
import org.lwjgl.opengl.*;
public class Test {
// Setup variables
private int WIDTH = 800;
private int HEIGHT = 600;
private String title = "Circle";
// Quad variables
private int vbo = 0; // Vertex Buffer Object
private int vao = 0; // Vertex Array Object
int SUBDIVISIONS = 100;
float[] vertex = new float[(SUBDIVISIONS + 1) * 4];
public Test() {
// Initialize
setupOpenGL();
setupQuad();
while (!Display.isCloseRequested()) {
loop();
Display.update();
Display.sync(60);
}
Display.destroy();
}
public void setupOpenGL() {
try {
Display.setDisplayMode(new DisplayMode(WIDTH, HEIGHT));
Display.setTitle(title);
Display.create();
} catch (LWJGLException e) {
e.printStackTrace();
System.exit(-1); // If error , exit program
}
GL11.glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
}
public void setupQuad() {
float r = 0.2f;
float x;
float y;
float offSetX = 0.3f;
float offSetY = 0.3f;
vertex[0] = (float) Math.sin(Math.PI*2*0/SUBDIVISIONS) * r + offSetX;
vertex[1] = (float) Math.cos(Math.PI*2*1/SUBDIVISIONS) * r + offSetY;
for (int i = 2; i < 360; i = i + 2) {
double angle = Math.PI * 2 * i / SUBDIVISIONS;
x = (float) Math.cos(angle) * r;
vertex[i] = x + offSetX;
}
for (int i = 3; i < 360; i = i + 2) {
double angle = Math.PI * 2 * i / SUBDIVISIONS;
y = (float) Math.sin(angle) * r;
vertex[i] = y + offSetY;
}
FloatBuffer vertexBuffer = BufferUtils.createFloatBuffer(vertex.length);
vertexBuffer.put(vertex);
vertexBuffer.flip();
vao = GL30.glGenVertexArrays();
GL30.glBindVertexArray(vao);
vbo = GL15.glGenBuffers();
GL15.glBindBuffer(GL15.GL_ARRAY_BUFFER, vbo);
GL15.glBufferData(GL15.GL_ARRAY_BUFFER,vertexBuffer,GL15.GL_STATIC_DRAW);
GL20.glVertexAttribPointer(0, 2, GL11.GL_FLOAT, false, 0, 0);
GL15.glBindBuffer(GL15.GL_ARRAY_BUFFER, 0);
GL30.glBindVertexArray(0);
}
public void loop() {
GL11.glClear(GL11.GL_COLOR_BUFFER_BIT);
GL30.glBindVertexArray(vao);
GL20.glEnableVertexAttribArray(0);
// Draw the vertices
GL11.glDrawArrays(GL11.GL_TRIANGLE_FAN, 0, vertex.length / 2);
// Put everything back to default (deselect)
GL20.glDisableVertexAttribArray(0);
GL30.glBindVertexArray(0);
}
public static void main(String[] args) {
new Test();
}
}
Solution
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