LWJGL 3不会画一条线

Question

我正在尝试用LWJGL 3绘制一条线.它编译并且所有原生设置都正确设置.我在Ubuntu上运行.我真的不明白问题是什么; 窗口初始化,背景是正确的清晰颜色,但线条不会绘制.我几乎完全从我在新网站上找到的唯一示例中复制了代码.我不知道我做错了什么.

import static org.lwjgl.glfw.GLFW.*;
import static org.lwjgl.opengl.GL11.*;
import static org.lwjgl.system.MemoryUtil.NULL;

import java.awt.DisplayMode;
import java.nio.ByteBuffer;

import org.lwjgl.glfw.GLFWErrorCallback;
import org.lwjgl.glfw.GLFWKeyCallback;
import org.lwjgl.glfw.GLFWvidmode;
import org.lwjgl.opengl.GL11;
import org.lwjgl.opengl.GLContext;
import org.lwjgl.util.Display;
import org.lwjgl.util.glu.GLU;

public class Main {
    // We need to strongly reference callback instances.
    private static GLFWErrorCallback errorCallback;
    private static GLFWKeyCallback   keyCallback;
    static final int INIT_WIDTH = 300;
    static final int INIT_HEIGHT = 300;

    // The window handle
    private static long window;

    public static boolean verbose = true;

    public static void init() {
        final String WINDOW_TITLE = "WINDOW";

        vPrint("Initializing GLFW...");
        if (glfwInit() != GL11.GL_TRUE) {
            throw new IllegalStateException("Unable to initialize GLFW");
        }
        vPrint("Done!\n");

        //Window will be hidden after creation
        glfwWindowHint(GLFW_VISIBLE, GL_FALSE);
        //Window will be resizable
        glfwWindowHint(GLFW_RESIZABLE, GL_TRUE);

        vPrint("Creating window...");
        window = glfwCreateWindow(INIT_WIDTH, INIT_HEIGHT, WINDOW_TITLE, NULL, NULL);
        if (window == NULL) {
            throw new RuntimeException("Failed to create the GLFW window");
        } else {
            vPrint("Done!\n");
        }

        //Setup a key callback. It will be called every time a key is pressed, repeated or released.
        glfwSetKeyCallback(window, keyCallback = new GLFWKeyCallback() {
            @Override
            public void invoke(long window, int key, int scancode, int action, int mods) {
                if ( key == GLFW_KEY_ESCAPE && action == GLFW_RELEASE )
                    glfwSetWindowShouldClose(window, GL_TRUE); // We will detect this in our rendering loop
            }
        });

        // Get the resolution of the primary monitor
        ByteBuffer vidmode = glfwGetVideoMode(glfwGetPrimaryMonitor());
        // Center our window
        glfwSetWindowPos(
            window,
            (GLFWvidmode.width(vidmode) - INIT_WIDTH) / 2,
            (GLFWvidmode.height(vidmode) - INIT_HEIGHT) / 2
        );

        // Make the OpenGL context current
        glfwMakeContextCurrent(window);
        // Enable v-sync
        glfwSwapInterval(1);

        // Make the window visible
        glfwShowWindow(window);
        GLContext.createFromCurrent();

        //Set window clear color
        glClearColor(0.5f, 0.0f, 0.0f, 0.0f);

        initOpenGL();
    }

    public static void main(String[] args) {
        try {
            init();
            loop();

            glfwDestroyWindow(window);
            keyCallback.release();
        } finally {
            glfwTerminate();
            errorCallback.release();
        }
    }

    public static void loop() {
        // Run the rendering loop until the user has attempted to close
        // the window or has pressed the ESCAPE key.
        while ( glfwWindowShouldClose(window) == GL_FALSE ) {
            glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // clear the framebuffer

            glfwSwapBuffers(window); // swap the color buffers
            render();

            // Poll for window events. The key callback above will only be
            // invoked during this call.
            glfwPollEvents();
        }
    }

    private static void vPrint(String str) {
        if (verbose) {
            System.out.print(str);
        }
    }

    private static void render() {
        glColor3f(1, 1, 1);
        glBegin(GL_LINE);
            glVertex2f(10, 10);
            glVertex2f(20, 20);
        glEnd();
    }

    private static void initOpenGL() {
         glViewport(0, 0, INIT_WIDTH, INIT_HEIGHT);
         glMatrixMode(GL_PROJECTION);
         glLoadIdentity();

         // Calculate The Aspect Ratio Of The Window
         GLU.gluPerspective(30.0f, (float)INIT_HEIGHT / (float)INIT_HEIGHT, 0.3f, 200.0f);

         glMatrixMode(GL_MODELVIEW);
         glLoadIdentity();
    }
}

编辑:我现在很确定这是我使用的错误GL_LINE;

Answer 1

这里有很多问题.

画电话

你有一个受欢迎但有时很难发现的错误:

glBegin(GL_LINE);

绘制线条的枚举是GL_LINES(注意尾随S).GL_LINE另一方面是可能的论据之一glPolygonMode().所以这个电话应该是:

glBegin(GL_LINES);

绘制循环中的调用顺序

渲染循环中的调用顺序看起来不对:

while ( glfwWindowShouldClose(window) == GL_FALSE ) {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glfwSwapBuffers(window);
    render();
    glfwPollEvents();
}

该glfwSwapBuffers()调用指定您已完成渲染,并准备呈现您呈现的内容.由于您在打电话之前正在进行该呼叫render(),因此所呈现的仅是已清除的缓冲区.

或者以不同的方式看待它,如果您在循环结束和开始之间逐步调用,并忽略glfwPollEvents()调用,render()则会立即跟随您的调用glClear().因此渲染的结果在它有机会被呈现之前被清除.

正确的呼叫顺序是:

while ( glfwWindowShouldClose(window) == GL_FALSE ) {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    render();
    glfwSwapBuffers(window);
    glfwPollEvents();
}

这将允许在结果与glfwSwapBuffers()调用一起显示之前执行渲染.

坐标范围

您需要注意变换和坐标范围.当您设置一个透视变换时,它将假设您的坐标位于从负原点向下看的近和远平面范围之间.作为模型视图矩阵的一部分,您将需要在负z方向上进行平移,以获得查看体积内的坐标.否则整个几何体将被剪掉.

例如,您可以glTranslatef()在设置模型视图矩阵时添加调用,该矩阵将几何体放置在近平面和远平面之间:

glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0.0f, 0.0f, -50.0f);

如果此解释不充分,您可能需要查找解释OpenGL坐标系和转换的教程.