[c++] 使用 raylib + ODE(open dynamics engine) 制作一个简易牛顿摆_c++ ode库

Raylib

raylib 是一个简单易用的2D/3D图形库。

ODE

open dynamics engine 是一个很老的高性能刚体物理运算库。

效果

代码

#include <vector>
#include <map>
#include "ode/ode.h"
#include "raylib.h"

int screenWidth = 1280;  // 窗口宽
int screenHeight = 720;  //窗口高
int fps = 60; // 帧率
int count = 15;  // 单摆数量
double interval = .001;  //每个小球之间的间隙
double phyicsStep = 0.0001;  // 每次物理运算经过的时间
int subStep = 300; // 每一帧物理运算次数

dWorldID world;
dJointGroupID contactgroup;
dSpaceID space;
dMass m1;
std::map<dGeomID, dJointID> g2j;
std::map<dGeomID, Color> g2c;
const dReal *pos, *R;

struct MyObject {
    dBodyID body;
    dGeomID geom;
    Model model;
    dReal size;
};

void nearCallback(void *data, dGeomID o1, dGeomID o2) {
    if (g2j.contains(o1) && g2j.contains(o2) && g2j[o1] == g2j[o2]) {
        return;
    }

    int N = 1;
    dContact contact[N];

    int n = dCollide(o1, o2, N, &contact[0].geom, sizeof(dContact));

    if (n > 0) {
        g2c[o1] = RED;
        g2c[o2] = RED;
    }

    for (int i = 0; i < n; i++) {
        contact[i].surface.mode = dContactBounce;
        contact[i].surface.mu = dInfinity;
        contact[i].surface.bounce = .99;
        contact[i].surface.bounce_vel = 0.;
        dJointID c = dJointCreateContact(world, contactgroup, &contact[i]);
        dJointAttach(c, dGeomGetBody(contact[i].geom.g1), dGeomGetBody(contact[i].geom.g2));
    }
}

void setTransform(const dReal R[12], Matrix *matrix) {
    matrix->m0 = float(R[0]);
    matrix->m1 = float(R[4]);
    matrix->m2 = float(R[8]);

    matrix->m4 = float(R[1]);
    matrix->m5 = float(R[5]);
    matrix->m6 = float(R[9]);

    matrix->m8 = float(R[2]);
    matrix->m9 = float(R[6]);
    matrix->m10 = float(R[10]);
}

struct MyJoint {
    MyObject ball;
    MyObject pole;
};

MyJoint createAobj(int i) {
    MyObject ball{
            .body = dBodyCreate(world),
            .size = 2.,
    };
    ball.model = LoadModelFromMesh(GenMeshSphere(float(ball.size), 9, 16));
    dMassSetZero(&m1);
    dMassSetSphereTotal(&m1, 1., ball.size);
    dBodySetMass(ball.body, &m1);
    dBodySetPosition(ball.body, (double(i) - double(count - 1) / 2.) * ball.size * (ball.size + interval), 4., 0.);
    ball.geom = dCreateSphere(space, ball.size);
    dGeomSetBody(ball.geom, ball.body);
    g2c[ball.geom] = WHITE;

    MyObject pole{
            .body = dBodyCreate(world),
            .size = 0.25,
    };
    pole.model = LoadModelFromMesh(GenMeshCube(float(pole.size), float(pole.size) * 40.f, float(pole.size)));
    dMassSetZero(&m1);
    dMassSetBoxTotal(&m1, .001, pole.size, pole.size * 40., pole.size);
    dBodySetMass(pole.body, &m1);
    dBodySetPosition(pole.body, (double(i) - double(count - 1) / 2.) * ball.size * (ball.size + interval), 0.5 * pole.size * 40. + ball.size + 4., 0.);
    pole.geom = dCreateBox(space, pole.size, pole.size * 40., pole.size);
    dGeomSetBody(pole.geom, pole.body);

    dJointID joint = dJointCreateHinge(world, nullptr);
    dJointAttach(joint, ball.body, pole.body);
    dJointSetHingeAnchor(joint, (double(i) - double(count - 1) / 2.) * ball.size * (ball.size + interval), ball.size + 4., 0.);
    dJointSetHingeAxis(joint, 0, 0, 1);

    g2j[pole.geom] = joint;
    g2j[ball.geom] = joint;

    dJointID jt = dJointCreateHinge(world, nullptr);
    dJointAttach(jt, pole.body, nullptr);
    dJointSetHingeAnchor(jt, (double(i) - double(count - 1) / 2.) * ball.size * (ball.size + interval), ball.size + 4. + pole.size * 40., 0.);
    dJointSetHingeAxis(jt, 0, 0, 1);

    return MyJoint{
            .ball = ball,
            .pole = pole,
    };
}

int main() {
    SetConfigFlags(FLAG_MSAA_4X_HINT);
    SetConfigFlags(FLAG_WINDOW_RESIZABLE);
    InitWindow(screenWidth, screenHeight, "raylib ODE");
    Camera3D camera = {0};
    camera.position = (Vector3) {0.f, 10.f, float((count + 5) * 2)};
    camera.target = (Vector3) {0.f, 10.f, 0.f};
    camera.up = (Vector3) {0.f, 1.f, 0.f};
    camera.fovy = 60.0f;
    camera.projection = CAMERA_PERSPECTIVE;
    SetCameraMode(camera, CAMERA_FREE);
    SetCameraAltControl(KEY_LEFT_SHIFT);
    SetCameraPanControl(MOUSE_BUTTON_RIGHT);
    SetTargetFPS(fps);

    dInitODE();
    world = dWorldCreate();
    space = dHashSpaceCreate(nullptr);
    contactgroup = dJointGroupCreate(0);

    dWorldSetGravity(world, 0., -98, 0.);

    std::vector<MyJoint> objs;
    for (int i = 0; i < count; ++i) {
        objs.push_back(createAobj(i));
    }

    while (!WindowShouldClose()) {
        for (int i = 0; i < subStep; ++i) {
            if (IsKeyDown(KEY_SPACE)) {
                dBodySetTorque(objs[0].pole.body, 0, 0, -300);
                dBodySetForce(objs[0].ball.body, -50, 10, 0);
            }

            dSpaceCollide(space, nullptr, &nearCallback);
            dWorldStep(world, phyicsStep);
            dJointGroupEmpty(contactgroup);
        }

        UpdateCamera(&camera);

        BeginDrawing();
        ClearBackground(BLACK);
        BeginMode3D(camera);

        for (auto &obj : objs) {
            pos = dBodyGetPosition(obj.ball.body);
            R = dBodyGetRotation(obj.ball.body);
            setTransform(R, &obj.ball.model.transform);

            DrawModelWires(obj.ball.model, Vector3{float(pos[0]), float(pos[1]), float(pos[2])}, 1.f, BLACK);
            DrawModel(obj.ball.model, Vector3{float(pos[0]), float(pos[1]), float(pos[2])}, 1.f, g2c[obj.ball.geom]);

            pos = dBodyGetPosition(obj.pole.body);
            R = dBodyGetRotation(obj.pole.body);
            setTransform(R, &obj.pole.model.transform);

            DrawModelWires(obj.pole.model, Vector3{float(pos[0]), float(pos[1]), float(pos[2])}, 1.f, BLACK);
            DrawModel(obj.pole.model, Vector3{float(pos[0]), float(pos[1]), float(pos[2])}, 1.f, WHITE);
        }

        EndMode3D();
        DrawFPS(10, 10);
        EndDrawing();

        for (auto &c : g2c) {
            c.second = WHITE;
        }
    }

    dWorldDestroy(world);
    dCloseODE();
    CloseWindow();

    return 0;
}
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编译

首先需要安装 raylib 和 ode，ArchLinux 可通过 pacman 直接安装：

sudo pacman -S raylib ode
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也要有 c++ 编译器，执行编译命令：

g++ -O2 -lraylib -lode --std=c++23 main.cpp
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执行生成的 a.out 即可。

操作

• 长按 鼠标右键 并 移动鼠标：拖动场景
• 按住 Shift，然后长按 鼠标右键 并 移动鼠标：旋转场景
• 长按 空格：拉起第一颗球