Linux 上的 SDL OpenGL 新手，这有什么问题吗？

Question

我已经编写了一些代码来在 Ubuntu 上试验 opengl 编程，虽然已经有一段时间了，但我曾经对 C 有一定的了解。由于我被告知 c++ 是游戏编程的首选语言，我正在尝试用它进行开发。

这是我第一次真正尝试使用 sdl 进行 opengl，到目前为止，它可以编译并运行，但我的相机功能似乎没有做任何事情。 我知道可能有很多更好的方法来做这类事情，但我想在继续更高级的事情之前先了解基础知识。

main.cpp

#include <iostream>
#include <cmath>
#include "SDL/SDL.h"
#include "SDL/SDL_opengl.h"

int screen_width = 640;
int screen_height = 480;
const int screen_bpp = 32;
float rotqube = 0.9f;

float xpos = 0, ypos = 0, zpos = 0, xrot = 0, yrot = 0, angle=0.0;
float lastx, lasty;

SDL_Surface *screen = NULL; // create a default sdl_surface to render our opengl to

void camera (void) {
glRotatef(xrot,1.0,0.0,0.0);  // x-axis (left and right)
glRotatef(yrot,0.0,1.0,0.0);  // y-axis (up and down)
glTranslated(-xpos,-ypos,-zpos); // translate the screen to the position
SDL_GL_SwapBuffers();
}

int DrawCube(void)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();

glTranslatef(0.0f, 0.0f,-7.0f);
glRotatef(rotqube,0.0f,1.0f,0.0f);
glRotatef(rotqube,1.0f,1.0f,1.0f);
glBegin(GL_QUADS);
    glColor3f(0.0f,1.0f,0.0f);
    glVertex3f( 1.0f, 1.0f,-1.0f);
    glVertex3f(-1.0f, 1.0f,-1.0f);
    glVertex3f(-1.0f, 1.0f, 1.0f);
    glVertex3f( 1.0f, 1.0f, 1.0f);
    glColor3f(1.0f,0.5f,0.0f);
    glVertex3f( 1.0f,-1.0f, 1.0f);
    glVertex3f(-1.0f,-1.0f, 1.0f);
    glVertex3f(-1.0f,-1.0f,-1.0f);
    glVertex3f( 1.0f,-1.0f,-1.0f);
    glColor3f(1.0f,0.0f,0.0f);
    glVertex3f( 1.0f, 1.0f, 1.0f);
    glVertex3f(-1.0f, 1.0f, 1.0f);
    glVertex3f(-1.0f,-1.0f, 1.0f);
    glVertex3f( 1.0f,-1.0f, 1.0f);
    glColor3f(1.0f,1.0f,0.0f);
    glVertex3f( 1.0f,-1.0f,-1.0f);
    glVertex3f(-1.0f,-1.0f,-1.0f);
    glVertex3f(-1.0f, 1.0f,-1.0f);
    glVertex3f( 1.0f, 1.0f,-1.0f);
    glColor3f(0.0f,0.0f,1.0f);
    glVertex3f(-1.0f, 1.0f, 1.0f);
    glVertex3f(-1.0f, 1.0f,-1.0f);
    glVertex3f(-1.0f,-1.0f,-1.0f);
    glVertex3f(-1.0f,-1.0f, 1.0f);
    glColor3f(1.0f,0.0f,1.0f);
    glVertex3f( 1.0f, 1.0f,-1.0f);
    glVertex3f( 1.0f, 1.0f, 1.0f);
    glVertex3f( 1.0f,-1.0f, 1.0f);
    glVertex3f( 1.0f,-1.0f,-1.0f);
glEnd();
SDL_GL_SwapBuffers();

rotqube +=0.9f;
return true;
}

bool init_sdl(void)
{
if( SDL_Init( SDL_INIT_EVERYTHING ) != 0 )
{
    return false;
}

SDL_GL_SetAttribute( SDL_GL_RED_SIZE, 5 );
SDL_GL_SetAttribute( SDL_GL_GREEN_SIZE, 5 );
SDL_GL_SetAttribute( SDL_GL_BLUE_SIZE, 5 );
SDL_GL_SetAttribute( SDL_GL_DEPTH_SIZE, 16 );
SDL_GL_SetAttribute( SDL_GL_DOUBLEBUFFER, 1 );

// TODO: Add error check to this screen surface init
screen = SDL_SetVideoMode( screen_width, screen_height, screen_bpp, SDL_OPENGL | SDL_HWSURFACE | SDL_RESIZABLE );

return true;
}

static void init_opengl()
{
float aspect = (float)screen_width / (float)screen_height;
glViewport(0, 0, screen_width, screen_height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(60.0, aspect, 0.1, 100.0);
glMatrixMode(GL_MODELVIEW);
glClearColor(0.0, 0.0 ,0.0, 0);
glEnable(GL_DEPTH_TEST);
}

void heartbeat()
{
float xrotrad, yrotrad;
int diffx, diffy;

SDL_Event event;

while(1)
{
    while(SDL_PollEvent(&event))
    {
        switch(event.type)
        {
            case SDL_KEYDOWN:
                switch(event.key.keysym.sym)
                {
                    case SDLK_ESCAPE:
                        exit(0);
                        break;
                    case SDLK_w:
                        yrotrad = (yrot / 180 * 3.141592654f);
                        xrotrad = (xrot / 180 * 3.141592654f);
                        xpos += (float)sin(yrotrad);
                        zpos -= (float)cos(yrotrad);
                        ypos -= (float)sin(xrotrad);
                        std::cout << "w pressed" << std::endl;
                        break;
                    case SDLK_s:
                        yrotrad = (yrot / 180 * 3.141592654f);
                        xrotrad = (xrot / 180 * 3.141592654f);
                        xpos -= (float)sin(yrotrad);
                        zpos += (float)cos(yrotrad);
                        ypos += (float)sin(xrotrad);
                        break;
                    case SDLK_d:
                        yrotrad = (yrot / 180 * 3.141592654f);
                        xpos += (float)cos(yrotrad) * 0.2;
                        zpos += (float)sin(yrotrad) * 0.2;
                            break;
                        case SDLK_a:
                        yrotrad = (yrot / 180 * 3.141592654f);
                        xpos -= (float)cos(yrotrad) * 0.2;
                        zpos -= (float)sin(yrotrad) * 0.2;
                            break;
                    default:
                        break;
                }
                break;

            case SDL_MOUSEMOTION:
                diffx=event.motion.x-lastx; //check the difference between the current x and the last x position
                diffy=event.motion.y-lasty; //check the difference between the current y and the last y position
                lastx=event.motion.x; //set lastx to the current x position
                lasty=event.motion.y; //set lasty to the current y position
                xrot += (float)diffy; //set the xrot to xrot with the addition of the difference in the y position
                yrot += (float)diffx;    //set the xrot to yrot with the addition of the difference in the x position
                break;

            case SDL_QUIT:
                exit(0);
                break;

            case SDL_VIDEORESIZE:
                screen = SDL_SetVideoMode( event.resize.w, event.resize.h, screen_bpp, SDL_OPENGL | SDL_HWSURFACE | SDL_RESIZABLE );
                screen_width = event.resize.w;
                screen_height = event.resize.h;
                init_opengl();
                std::cout << "Resized to width: " << event.resize.w << " height: " << event.resize.h << std::endl;
                break;

            default:
                break;
        }
    }

    DrawCube();
    camera();

    SDL_Delay( 50 );
}
}

int main(int argc, char* argv[])
{
if( init_sdl() != false )
{
    std::cout << "SDL Init Successful" << std::endl;
}

init_opengl();

std::cout << "Hello World" << std::endl;

heartbeat();    // this is essentially the main loop

SDL_Quit();

return 0;
}

Makefile

all:
g++ -o test main.cpp -lSDL -lGL -lGLU

它编译并运行，我想我只需要一些帮助来进行相机翻译。 谢谢

Answer 1

从 DrawCube() 中删除 glLoadIdentity() 调用。 将其替换为开头的 glPushMatrix() 和结尾的 glPopMatrix()。 现在按“w”会执行一些操作。 （我不完全确定它应该做什么。）

问题是 glLoadIdentity 清除了以前使用 glTranslatef 等设置的所有转换。 详细说明：http://www.opengl .org/documentation/specs/man_pages/hardcopy/GL/html/gl/pushmatrix.html

Answer 2

在绘制立方体之前尝试渲染相机。 现在相机平移工作正常，但是您正在相对于相机的相同位置绘制立方体。 如果您先绘制立方体，然后移动相机，您应该会看到您期望的翻译。