我的计算机运行带有Intel显卡的Ubuntu 16.04。我将Mesa 11.2用于我的OpenGL配置文件。
我不起眼的OpenGL程序在窗口中显示一个简单的正方形。如果要按某个键，我想使程序在线框模式之间切换，因此我定义了以下回调函数:
void keyCallback(GLFWwindow *window, int key, int scancode, int action, int mode) {
if (key == GLFW_KEY_ESCAPE and action == GLFW_PRESS) {
glfwSetWindowShouldClose(window, GL_TRUE);
}
if (key == GLFW_KEY_M and action == GLFW_PRESS) {
// Find the rasterizing mode.
GLint rastMode;
glGetIntegerv(GL_POLYGON_MODE, &rastMode);
// Switch modes depending on current rasterizing mode.
if (rastMode == GL_FILL) {
glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
}
else {
glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
}
}
}
不幸的是，在我的程序运行时按m会导致段错误。但是奇怪的是，在我的另一台计算机上(运行Ubuntu 16.04，但带有Nvidia GPU)，我没有出现此类问题，并且程序可以按预期运行。
问题不在于
glPolygonMode:我可以将其放在main函数中，程序将成功切换模式。问题似乎在于glGetIntegerv。如果我在main函数内部调用该函数(例如，在游戏循环外部)，则我的方块将拒绝出现(尽管没有segfault)。这是完整的代码:
#include <array>
#include <fstream>
#include <iostream>
#include <sstream>
#include <string>
#include <GL/glew.h>
#include <GLFW/glfw3.h>
// Vertex and fragment shader source files.
constexpr char VERTEX_SHADER_SOURCE_FILE[] = "simple_vertex.shader";
constexpr char FRAGMENT_SHADER_SOURCE_FILE[] = "simple_fragment.shader";
// Window properties.
constexpr int WINDOW_WIDTH = 800;
constexpr int WINDOW_HEIGHT = 800;
constexpr char WINDOW_TITLE[] = "Triangle";
// Background colour.
constexpr std::array<GLfloat, 4> bgColour { 0.3f, 0.1f, 0.3f, 1.0f };
/*
* Instructs GLFW to close window if escape key is pressed and to toggle between rasterizing modes
* if m is pressed.
*/
void keyCallback(GLFWwindow *window, int key, int scancode, int action, int mode);
int main() {
// Initialize GLFW.
if (not glfwInit()) {
std::cerr << "ERROR: Failed to start GLFW.\n";
return 1;
}
// Set required OpenGL version.
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
// Create a window object and bind it to the current context.
GLFWwindow *window = glfwCreateWindow(WINDOW_WIDTH, WINDOW_HEIGHT, WINDOW_TITLE, nullptr,
nullptr);
if (not window) {
std::cerr << "ERROR: Failed to create GLFW window.\n";
glfwTerminate();
return 1;
}
glfwMakeContextCurrent(window);
// Set callback functions.
glfwSetKeyCallback(window, keyCallback);
// Initialize GLEW with experimental features enabled.
glewExperimental = GL_TRUE;
if (glewInit() != GLEW_OK) {
std::cerr << "ERROR: Failed to start GLEW.\n";
glfwTerminate();
return 1;
}
// Display information on the current GL connection.
std::cout << "Renderer: " << glGetString(GL_RENDERER) << std::endl;
std::cout << "Version: " << glGetString(GL_VERSION) << std::endl;
std::cout << "Shading Language: " << glGetString(GL_SHADING_LANGUAGE_VERSION) << std::endl;
// Define the viewport dimensions.
int width, height;
glfwGetFramebufferSize(window, &width, &height);
glViewport(0, 0, static_cast<GLsizei>(width), static_cast<GLsizei>(height));
// Create a vertex shader object.
GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
// Load the vertex shader source code.
std::string vertexShaderSource;
std::ifstream vsfs(VERTEX_SHADER_SOURCE_FILE);
if (vsfs.is_open()) {
std::stringstream ss;
ss << vsfs.rdbuf();
vertexShaderSource = ss.str();
}
else {
std::cerr << "ERROR: File " << VERTEX_SHADER_SOURCE_FILE << " could not be found.\n";
glfwTerminate();
return 1;
}
// Attach the shader source code to the vertex shader object and compile.
const char *vertexShaderSource_cstr = vertexShaderSource.c_str();
glShaderSource(vertexShader, 1, &vertexShaderSource_cstr, nullptr);
glCompileShader(vertexShader);
// Check if compilation was successful.
GLint success;
glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
if (not success) {
std::cerr << "ERROR: Vertex shader compilation failed.\n";
glfwTerminate();
return 1;
}
// Create a fragment shader object.
GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
// Load the fragment shader source code.
std::string fragmentShaderSource;
std::ifstream fsfs(FRAGMENT_SHADER_SOURCE_FILE);
if (fsfs.is_open()) {
std::stringstream ss;
ss << fsfs.rdbuf();
fragmentShaderSource = ss.str();
}
else {
std::cerr << "ERROR: File " << FRAGMENT_SHADER_SOURCE_FILE << " could not be found.\n";
glfwTerminate();
return 1;
}
// Attach the shader source code to the fragment shader object and compile.
const char *fragmentShaderSource_cstr = fragmentShaderSource.c_str();
glShaderSource(fragmentShader, 1, &fragmentShaderSource_cstr, nullptr);
glCompileShader(fragmentShader);
// Check if compilation was successful.
glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
if (not success) {
std::cerr << "ERROR: Fragment shader compilation failed.\n";
glfwTerminate();
return 1;
}
// Link the vertex and fragment shaders into a shader program.
GLuint shaderProgram = glCreateProgram();
glAttachShader(shaderProgram, vertexShader);
glAttachShader(shaderProgram, fragmentShader);
glLinkProgram(shaderProgram);
// Check that shader program was successfully linked.
glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
if (not success) {
std::cerr << "ERROR: Shader program linking failed.\n";
glfwTerminate();
return 1;
}
// Delete shader objects.
glDeleteShader(vertexShader);
glDeleteShader(fragmentShader);
// Coordinates of square's vertices.
std::array<GLfloat, 12> vertices {
0.5f, 0.5f, 0.0f,
0.5f, -0.5f, 0.0f,
-0.5f, -0.5f, 0.0f,
-0.5f, 0.5f, 0.0f
};
// Indices to draw.
std::array<GLuint, 6> indices {
0, 1, 3,
1, 2, 3
};
// Create a vertex array object.
GLuint vao;
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
// Create a vertex buffer object.
GLuint vbo;
glGenBuffers(1, &vbo);
glBindBuffer(GL_ARRAY_BUFFER, vbo);
// Create an element buffer object.
GLuint ebo;
glGenBuffers(1, &ebo);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo);
// Pass vertex data into currently bound vertex buffer object.
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices.data(), GL_STATIC_DRAW);
// Pass index data into currently bound element buffer object.
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices.data(), GL_STATIC_DRAW);
// Create and enable a vertex attribute.
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), static_cast<GLvoid*>(0));
glEnableVertexAttribArray(0);
// It is good practice to unbind the vertex array object, vertex buffer object, and element
// buffer object.
glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
glBindVertexArray(0);
// Set background colour.
glClearColor(bgColour[0], bgColour[1], bgColour[2], bgColour[3]);
// Main loop.
while (not glfwWindowShouldClose(window)) {
// Clear the screen of colours and poll for events.
glClear(GL_COLOR_BUFFER_BIT);
glfwPollEvents();
// Inform OpenGL to use the shader program created above.
glUseProgram(shaderProgram);
// Bind the vertex array object and element buffer object.
glBindVertexArray(vao);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo);
// Draw the triangle using glDrawElements. The first argument gives the OpenGL primitive to
// render, the second argument gives the number of vertices to draw, the third gives type
// used to represent an index, and finally the last argument gives a possible offset in the
// EBO.
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, static_cast<GLvoid*>(0));
// Unbind the vertex array object (good practice).
glBindVertexArray(0);
// Swap buffers.
glfwSwapBuffers(window);
}
// Clean up.
glDeleteVertexArrays(1, &vao);
glDeleteBuffers(1, &vbo);
glDeleteProgram(shaderProgram);
glfwDestroyWindow(window);
glfwTerminate();
return 0;
}
void keyCallback(GLFWwindow *window, int key, int scancode, int action, int mode) {
if (key == GLFW_KEY_ESCAPE and action == GLFW_PRESS) {
glfwSetWindowShouldClose(window, GL_TRUE);
}
if (key == GLFW_KEY_M and action == GLFW_PRESS) {
// Find the rasterizing mode.
GLint rastMode;
glGetIntegerv(GL_POLYGON_MODE, &rastMode);
// Switch modes depending on current rasterizing mode.
if (rastMode == GL_FILL) {
glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
}
else {
glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
}
}
}
最佳答案
文档说:
总结@Wyzard和我的评论:glGetIntegerv(GL_POLYGON_MODE, &rastMode);需要两个整数的内存才能写入。该段错误是由于编写了过去的rastMode int
解决方案是传递两个整数的缓冲区。
关于c++ - OpenGL:切换多边形模式会导致段错误，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/37115829/