OpenGL Triange 演示显示空白窗口

Question

我从一个三角形演示开始学习 LWJGL3 和 OpenGL 3.2+。该程序似乎运行良好，我没有收到任何 OpenGL 错误，但三角形没有出现在屏幕上。

我已经查看了此处的一些类似问题，其中许多已确定的问题是缺少 VAO 或错误的三角坐标或着色器，但我已经在我的代码中检查了这些问题。创建 VAO，绑定并分配顶点属性。三角形坐标实际上应该构成一个三角形，我的着色器say它们已经正确编译和链接。我对我在这里错过的东西感到茫然。

这是我的代码。一切都在这个文件中（三角形顶点数据、OpenGL 对象 ID 和底部的着色器源代码），除了 LWJGL 本身和我用于我的矩阵的 com.hackoeur.jglm 库：

package net.part1kl;

import com.hackoeur.jglm.Mat4;
import com.hackoeur.jglm.Matrices;
import org.lwjgl.Version;
import org.lwjgl.glfw.*;
import static org.lwjgl.glfw.GLFW.*;
import org.lwjgl.opengl.GL;
import java.nio.FloatBuffer;
import java.nio.IntBuffer;
import static org.lwjgl.opengl.GL30C.*;
import static org.lwjgl.system.MemoryUtil.*;


public class Demo {

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

    private static long window;

    private static void init(){
        /* Initialize GLFW */
        System.out.println(Version.getVersion());
        glfwSetErrorCallback(GLFWErrorCallback.createPrint(System.err));
        if (!glfwInit()) throw new IllegalStateException("GLFW Init Failed");

        /* Set window hints and create window */
        glfwDefaultWindowHints();
        glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
        glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 2);
        glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
        glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GLFW_TRUE);
        glfwWindowHint(GLFW_RESIZABLE, GLFW_FALSE);
        glfwWindowHint(GLFW_VISIBLE, GLFW_FALSE);
        window = glfwCreateWindow(600, 600, "Demo", NULL, NULL);
        if ( window == NULL) { glfwTerminate(); throw new RuntimeException("Window Creation Failed"); }

        /* Other window setup */
        glfwSetWindowPos(window, 200, 200);
        glfwMakeContextCurrent(window);
        GL.createCapabilities();
        glfwSwapInterval(1);
        glfwSetKeyCallback(window, (window, key, scancode, action, mods) -> {
            if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS) glfwSetWindowShouldClose(window, true);
        });
        glfwShowWindow(window);

        /* Create and bind VAO */
        vao = glGenVertexArrays();
        glBindVertexArray(vao);

        /* Create, bind, and populate VBO */
        vbo = glGenBuffers();
        glBindBuffer(GL_ARRAY_BUFFER, vbo);
        FloatBuffer verts = memAllocFloat(vertices.length);
        for (float val : vertices) verts.put(val);
        verts.flip();
        glBufferData(GL_ARRAY_BUFFER, verts, GL_STATIC_DRAW);
        memFree(verts);

        /* Create Vertex Shader */
        vShader = glCreateShader(GL_VERTEX_SHADER);
        glShaderSource(vShader, vertexSource);
        glCompileShader(vShader);
        if (glGetShaderi(vShader, GL_COMPILE_STATUS) != GL_TRUE) throw new RuntimeException(glGetShaderInfoLog(vShader));

        /* Create Fragment Shader */
        fShader = glCreateShader(GL_FRAGMENT_SHADER);
        glShaderSource(fShader, fragmentSource);
        glCompileShader(fShader);
        if (glGetShaderi(fShader, GL_COMPILE_STATUS) != GL_TRUE) throw new RuntimeException(glGetShaderInfoLog(fShader));

        /* Create Shader Program */
        program = glCreateProgram();
        glAttachShader(program, vShader);
        glAttachShader(program, fShader);
        glBindFragDataLocation(program, 0, "fragColor");
        glLinkProgram(program);
        if (glGetProgrami(program, GL_LINK_STATUS) != GL_TRUE) throw new RuntimeException(glGetProgramInfoLog(program));
        glUseProgram(program);

        /* Set pointer for vertex position information */
        int pAttr = glGetAttribLocation(program, "position");
        glEnableVertexAttribArray(pAttr);
        glVertexAttribPointer(pAttr, 3, GL_FLOAT, false, 6 * Float.BYTES, 0);

        /* Set pointer for vertex color information */
        int cAttr = glGetAttribLocation(program, "color");
        glEnableVertexAttribArray(cAttr);
        glVertexAttribPointer(cAttr, 3, GL_FLOAT, false, 6 * Float.BYTES, 3 * Float.BYTES);

        /* Create and set model uniform. Using com.hackoeur.jglm v1.0.0 for matrices. */
        Mat4 model = new Mat4();
        int uModel = glGetUniformLocation(program, "model");
        glUniformMatrix4fv(uModel, false, (FloatBuffer)model.getBuffer().flip());

        /* Create and set view uniform */
        Mat4 view = new Mat4();
        int uView = glGetUniformLocation(program, "view");
        glUniformMatrix4fv(uView, false, (FloatBuffer)view.getBuffer().flip());

        /* Get window size ratio for projection */
        IntBuffer width = memAllocInt(1);
        IntBuffer height = memAllocInt(1);
        GLFW.glfwGetFramebufferSize(window, width, height);
        float ratio = width.get() / (float) height.get();
        memFree(width); memFree(height);

        /* Create and set projection uniform */
        Mat4 projection = Matrices.ortho(-ratio, ratio, -1f, 1f, -1f, 1f);
        int uProjection = glGetUniformLocation(program, "projection");
        glUniformMatrix4fv(uProjection, false, (FloatBuffer)projection.getBuffer().flip());
    }

    private static void loop(){
        double lastTime = glfwGetTime();
        double time = lastTime;
        while(!glfwWindowShouldClose(window)){
            double delta = (float) (time - lastTime);

            glClear(GL_COLOR_BUFFER_BIT);

            glBindVertexArray(vao);
            glBindBuffer(GL_ARRAY_BUFFER, vbo);
            glUseProgram(program);


            glDrawArrays(GL_TRIANGLES, 0, 3);

            glfwSwapBuffers(window);
            glfwPollEvents();

            glCheck();

            lastTime = time;
            time = glfwGetTime();
        }
    }

    private static void dispose(){
        glDeleteVertexArrays(vao);
        glDeleteBuffers(vbo);
        glDeleteShader(vShader);
        glDeleteShader(fShader);
        glDeleteProgram(program);

        glfwDestroyWindow(window);
    }

    private static void print(String message) { System.out.println(message); }

    private static void err(String message) { System.err.println(message); }

    private static int glCheckCounter = 0;

    private static void glCheck() {
        int val = glGetError();
        if (val==0) print("GL Error Check "+glCheckCounter+" no error.");
        else err("GL Error Check "+glCheckCounter+" returned error "+val);
        glCheckCounter++;
    }


    private static int vao, vbo, vShader, fShader, program;
    private static final float[] vertices = {
            -0.6f,   -0.4f,   0f,   1f,   0f,   0f,
             0.6f,   -0.4f,   0f,   0f,   1f,   0f,
               0f,    0.6f,   0f,   0f,   0f,   1f
    };
    private static final CharSequence vertexSource
            = "#version 150 core\n"
            + "\n"
            + "in vec3 position;\n"
            + "in vec3 color;\n"
            + "\n"
            + "out vec3 vertexColor;\n"
            + "\n"
            + "uniform mat4 model;\n"
            + "uniform mat4 view;\n"
            + "uniform mat4 projection;\n"
            + "\n"
            + "void main() {\n"
            + "    vertexColor = color;\n"
            + "    mat4 mvp = projection * view * model;\n"
            + "    gl_Position = mvp * vec4(position, 1.0);\n"
            + "}";
    private static final CharSequence fragmentSource
            = "#version 150 core\n"
            + "\n"
            + "in vec3 vertexColor;\n"
            + "\n"
            + "out vec4 fragColor;\n"
            + "\n"
            + "void main() {\n"
            + "    fragColor = vec4(vertexColor, 1.0);\n"
            + "}";
}

这是我运行这个程序得到的输出：

3.3.1 build 7
GL Error Check 0 no error.
GL Error Check 1 no error.
GL Error Check 2 no error.
GL Error Check 3 no error.
GL Error Check 4 no error.
GL Error Check 5 no error.
GL Error Check 6 no error.
GL Error Check 7 no error.

“GL Error Check #no error”。只要程序运行，它就会一直运行，我已经在 8 个循环处将其切断。它从未出现过 OpenGL 错误。

Answer 1

问题似乎出在 init() 方法中设置的投影矩阵上。具体来说，投影矩阵是使用 GLFW 帧缓冲区大小而不是窗口大小来计算的。这可能会导致投影矩阵不正确，导致三角形被渲染到屏幕外。

要解决此问题，您可以更改行：

GLFW.glfwGetFramebufferSize(window, width, height);

至：

GLFW.glfwGetWindowSize(window, width, height);

这将为您提供计算投影矩阵时使用的正确窗口大小。

您的代码中似乎缺少的一件事是创建和绑定 OpenGL 帧缓冲区。在开始渲染到屏幕之前，您需要创建一个帧缓冲区对象 (FBO) 并绑定它。

以下是如何创建和绑定 FBO 的示例：

int fbo = glGenFramebuffers();
glBindFramebuffer(GL_FRAMEBUFFER, fbo);

您可以在创建窗口并初始化 OpenGL 后调用这些函数。

此外，请确保将视口设置为循环中窗口的正确大小。您可以使用 glViewport 来设置视口大小。

int width = 600;
int height = 600;
glViewport(0, 0, width, height);

你应该在循环中开始渲染你的三角形之前调用这个函数。

尝试将这些更改添加到您的代码中，看看三角形是否出现在屏幕上。