c++ - OpenGL 有时会绘制三角形，有时只是其中的一部分

Question

我用 C++ 和 OpenGL 编写了一个程序。这应该画一个黑色的三角形。它经常以正确的方式绘制三角形，但有时看起来不正确。

这是目标:

有两个罕见的错误结果:

主要功能:

int main(void)
{
    // Initialise GLFW
    if (!glfwInit())
    {
        fprintf(stderr, "Failed to initialize GLFW\n");
        return -1;
    }

glfwWindowHint(GLFW_SAMPLES, 4);
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 2);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 1);

// Open a window and create its OpenGL context
window = glfwCreateWindow(700, 700, "Arkanoid", NULL, NULL);
if (window == NULL){
    fprintf(stderr, "Failed to open GLFW window. If you have an Intel GPU, they are not 3.3 compatible. Try the 2.1 version of the tutorials.\n");
    glfwTerminate();
    return -1;
}
glfwMakeContextCurrent(window);

// Initialize GLEW
if (glewInit() != GLEW_OK) {
    fprintf(stderr, "Failed to initialize GLEW\n");
    return -1;
}

// Dark blue background
glClearColor(0.0f, 0.0f, 0.8f, 0.0f);

programID = LoadShaders("TransformVertexShader.vertexshader", "ColorFragmentShader.fragmentshader");

vertexPosition_modelspaceID = glGetAttribLocation(programID, "vertexPosition_modelspace");
vertexColorID = glGetAttribLocation(programID, "vertexColor");

glfwSetCursorPosCallback(window, mouseMove);

game = new Game();
game->vertexPosition_modelspaceID = vertexPosition_modelspaceID;
game->vertexColorID = vertexColorID;

game->prepareToDrawBoardBorderElement();

posXId = glGetUniformLocation(programID, "posX");
posYId = glGetUniformLocation(programID, "posY");

do {
    glClear(GL_COLOR_BUFFER_BIT);
    glUseProgram(programID);

    glEnableVertexAttribArray(vertexPosition_modelspaceID);
    glEnableVertexAttribArray(vertexColorID);

    glUniform1f(posXId, 0.0f);
    glUniform1f(posYId, 0.0f); 
    game->drawBoardBorders();

    glDisableVertexAttribArray(vertexPosition_modelspaceID);
    glDisableVertexAttribArray(vertexColorID);

    glfwSwapBuffers(window);
    glfwPollEvents();
} while (glfwGetKey(window, GLFW_KEY_ESCAPE) != GLFW_PRESS && glfwWindowShouldClose(window) == 0);

glDeleteBuffers(1, &vertexbuffer);
glDeleteProgram(programID);

glfwTerminate();

return 0;

Game.cpp 文件如下所示:

void Game::drawBoardBorders() 
{
    glDrawArrays(GL_TRIANGLES, 0, 3);
}

void Game::prepareToDrawBoardBorderElement()
{   
std::cout << "prepareToDrawBoardBorderElement \n";

g_vertex_buffer_data[0] = -1.0f;
g_vertex_buffer_data[1] =  1.0f;
g_vertex_buffer_data[2] =  0.0f;

g_vertex_buffer_data[3] = -0.5f;
g_vertex_buffer_data[4] =  1.0f;
g_vertex_buffer_data[5] =  0.0f;

g_vertex_buffer_data[6] = -1.0f;
g_vertex_buffer_data[7] =  0.0f;
g_vertex_buffer_data[8] =  0.0f;

for (int i = 0; i < 8; i++) {
    g_color_buffer_data[i] = 0.0f;
}

glGenBuffers(1, &vertexbuffer);
glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(g_vertex_buffer_data), g_vertex_buffer_data, GL_STATIC_DRAW);
glVertexAttribPointer(
    vertexPosition_modelspaceID, // The attribute we want to configure
    3,                  // size
    GL_FLOAT,           // type
    GL_FALSE,           // normalized?
    0,                  // stride
    (void*)0            // array buffer offset
    );

glGenBuffers(1, &colorbuffer);
glBindBuffer(GL_ARRAY_BUFFER, colorbuffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(g_color_buffer_data), g_color_buffer_data, GL_STATIC_DRAW);
glVertexAttribPointer(
    vertexColorID,               // The attribute we want to configure
    3,                           // size
    GL_FLOAT,                    // type
    GL_FALSE,                    // normalized?
    0,                           // stride
    (void*)0                     // array buffer offset
    );
// All of the above information you only need to specify to openGL once, not every time you draw a frame!
}

为什么有时我会得到意想不到的结果？我应该怎么做才能使其正常工作？

Answer 1

您在 g_color_buffer_data 中将一个元素初始化为少数。

这段代码:

for (int i = 0; i < 8; i++) {
   g_color_buffer_data[i] = 0.0f;
}

仅初始化数组的前 8 个元素，但绘制三个角点将需要 9 个颜色 float ，因为您按顶点使用 3 个 float (rgb)。

另一个提示:您正在使用非常好的现代 OpenGL。请注意，从 OpenGL 3.3 Core Profile 开始，必须使用 VertexArrayObjects。参见示例 this link (section Vertex Data) .这不会影响此处描述的问题，而应仅作为 future 工作的附加信息。