Java中OpenGL3通过蒙版绘制平面空心圆

要绘制平面空心圆，可以使用OpenGL的GL_LINES和GL_LINE_LOOP模式来绘制圆的边界线。其中，GL_LINES模式可以绘制两个点之间的线段，而GL_LINE_LOOP模式可以绘制连接所有点的闭合线段。

以下是一个简单的OpenGL3程序，它使用GL_LINE_LOOP模式绘制平面空心圆：

import org.lwjgl.opengl.GL;
import org.lwjgl.opengl.GL33;
import org.lwjgl.opengl.GLUtil;
import org.lwjgl.system.MemoryStack;
import org.lwjgl.system.MemoryUtil;

import java.nio.FloatBuffer;

public class CircleRenderer {
    private int vaoId;
    private int vboId;
    private int shaderProgramId;

    public CircleRenderer() {
        // 初始化OpenGL
        GL.createCapabilities();
        GLUtil.setupDebugMessageCallback();

        // 编译着色器程序
        shaderProgramId = compileShaderProgram();

        // 创建VAO和VBO
        vaoId = GL33.glGenVertexArrays();
        vboId = GL33.glGenBuffers();

        // 绑定VAO和VBO
        GL33.glBindVertexArray(vaoId);
        GL33.glBindBuffer(GL33.GL_ARRAY_BUFFER, vboId);

        // 设置顶点数据
        float[] vertices = getCircleVertices(0.5f, 32);
        FloatBuffer vertexBuffer = MemoryUtil.memAllocFloat(vertices.length);
        vertexBuffer.put(vertices).flip();
        GL33.glBufferData(GL33.GL_ARRAY_BUFFER, vertexBuffer, GL33.GL_STATIC_DRAW);
        GL33.glVertexAttribPointer(0, 2, GL33.GL_FLOAT, false, 0, 0);
        GL33.glEnableVertexAttribArray(0);

        // 解绑VAO和VBO
        GL33.glBindVertexArray(0);
        GL33.glBindBuffer(GL33.GL_ARRAY_BUFFER, 0);
    }

    public void render() {
        // 使用着色器程序
        GL33.glUseProgram(shaderProgramId);

        // 绑定VAO
        GL33.glBindVertexArray(vaoId);

        // 绘制圆
        GL33.glDrawArrays(GL33.GL_LINE_LOOP, 0, 33);

        // 解绑VAO
        GL33.glBindVertexArray(0);

        // 停用着色器程序
        GL33.glUseProgram(0);
    }

    private int compileShaderProgram() {
        int vertexShaderId = GL33.glCreateShader(GL33.GL_VERTEX_SHADER);
        GL33.glShaderSource(vertexShaderId, "#version 330 core\n"
                + "layout (location = 0) in vec2 aPos;\n"
                + "void main() {\n"
                + "  gl_Position = vec4(aPos.x, aPos.y, 0.0, 1.0);\n"
                + "}\n");
        GL33.glCompileShader(vertexShaderId);

        int fragmentShaderId = GL33.glCreateShader(GL33.GL_FRAGMENT_SHADER);
        GL33.glShaderSource(fragmentShaderId, "#version 330 core\n"
                + "out vec4 FragColor;\n"
                + "void main() {\n"
                + "  FragColor = vec4(1.0, 1.0, 1.0, 1.0);\n"
                + "}\n");
        GL33.glCompileShader(fragmentShaderId);

        int shaderProgramId = GL33.glCreateProgram();
        GL33.glAttachShader(shaderProgramId, vertexShaderId);
        GL33.glAttachShader(shaderProgramId, fragmentShaderId);
        GL33.glLinkProgram(shaderProgramId);

        GL33.glDeleteShader(vertexShaderId);
        GL33.glDeleteShader(fragmentShaderId);

        return shaderProgramId;
    }

    private float[] getCircleVertices(float radius, int segments) {
        float[] vertices = new float[(segments + 1) * 2];

        for (int i = 0; i <= segments; i++) {
            float angle = (float) (i * 2 * Math.PI / segments);
            vertices[i * 2] = radius * (float) Math.cos(angle);
            vertices[i * 2 + 1] = radius * (float) Math.sin(angle);
        }

        return vertices;
    }

    public void cleanup() {
        GL33.glDeleteProgram(shaderProgramId);
        GL33.glDeleteBuffers(vboId);
        GL33.glDeleteVertexArrays(vaoId);
    }
}

该程序使用GL_LINE_LOOP模式绘制32个点组成的圆。首先，它使用getCircleVertices方法生成圆的顶点坐标，然后将其存储在VBO中。接下来，它使用着色器程序和VAO绘制圆。

需要注意的是，该程序使用了LWJGL库来调用OpenGL函数。如果你不熟悉LWJGL，可以参考官方文档或其他教程。