D3D中的粒子系统（6）

14.3.3 例子程序：粒子枪

本例程实现了一个粒子枪系统，运行效果如图14.4所示：

下面是粒子枪系统的定义：
class cParticleGun : public cParticleSystem
{
private:
cCamera* m_camera;
public:
cParticleGun(cCamera* camera);
virtual void reset_particle(sParticleAttribute* attr);
virtual void update(float time_delta);
};

构造函数需要提供一个照相机的位置点，这是因为系统需要知道照相机的位置及朝向，以决定在哪创建一个粒子。
cParticleGun::cParticleGun(cCamera* camera)
{
m_camera = camera;
m_size = 0.8f;
m_vb_num = 2048;
m_vb_offset = 0;
m_vb_batch_num = 512;
}

reset_particle方法设置粒子的位置为当前照相机的位置，并且设置粒子运动的速度为照像机方向的100倍。这样，子弹将射向我们正在看的方向，粒子颜色为绿色。
void cParticleGun::reset_particle(sParticleAttribute* attr)
{
attr->is_alive = true;
D3DXVECTOR3 camera_dir;
m_camera->get_look(&camera_dir);
attr->position = m_camera->m_pos; // change to camera position
attr->position.y -= 1.0f; // sightly below camera so it looks like we're carrying a gun
// travels in the direction the camera is looking
attr->velocity = camera_dir * 100.0f;
attr->color = D3DXCOLOR(0.0f, 1.0f, 0.0f, 1.0f); // green
attr->age = 0.0f;
attr->life_time = 1.0f; // lives for 1 seconds
}

update方法更新粒子的位置，并且杀死超过其生命周期的粒子，然后，我们搜索粒子列表删除已经死了的粒子。
void cParticleGun::update(float time_delta)
{
for(list<sParticleAttribute>::iterator iter = m_particles.begin(); iter != m_particles.end(); iter++)
{
iter->position += iter->velocity * time_delta;
iter->age += time_delta;
if(iter->age > iter->life_time)
iter->is_alive = false; // kill
}
remove_dead_particles();
}

执行程序：
#include "d3dUtility.h"
#include "camera.h"
#include "ParticleSystem.h"
#include <cstdlib>
#include <ctime>
#pragma warning(disable : 4100)
const int WIDTH = 640;
const int HEIGHT = 480;
IDirect3DDevice9* g_device;
cParticleSystem* g_gun;
cCamera g_camera(AIR_CRAFT);
////////////////////////////////////////////////////////////////////////////////////////////////////
bool setup()
{
srand((unsigned int)time(NULL));
// create laser
g_gun = new cParticleGun(&g_camera);
g_gun->init(g_device, "flare_alpha.dds");
// setup a basic scnen, the scene will be created the first time this function is called.
draw_basic_scene(g_device, 1.0f);
// set the projection matrix
D3DXMATRIX proj;
D3DXMatrixPerspectiveFovLH(&proj, D3DX_PI/4.0f, (float)WIDTH/HEIGHT, 1.0f, 1000.0f);
g_device->SetTransform(D3DTS_PROJECTION, &proj);
return true;
}
///////////////////////////////////////////////////////////////////////////////////////////////////////
void cleanup()
{
delete g_gun;
// pass NULL for the first parameter to instruct cleanup
draw_basic_scene(NULL, 1.0f);
}
///////////////////////////////////////////////////////////////////////////////////////////////////////
bool display(float time_delta)
{
// update the camera
if( GetAsyncKeyState(VK_UP) & 0x8000f )
g_camera.walk(4.0f * time_delta);
if( GetAsyncKeyState(VK_DOWN) & 0x8000f )
g_camera.walk(-4.0f * time_delta);
if( GetAsyncKeyState(VK_LEFT) & 0x8000f )
g_camera.yaw(-1.0f * time_delta);
if( GetAsyncKeyState(VK_RIGHT) & 0x8000f )
g_camera.yaw(1.0f * time_delta);
if( GetAsyncKeyState('N') & 0x8000f )
g_camera.strafe(-4.0f * time_delta);
if( GetAsyncKeyState('M') & 0x8000f )
g_camera.strafe(4.0f * time_delta);
if( GetAsyncKeyState('W') & 0x8000f )
g_camera.pitch(1.0f * time_delta);
if( GetAsyncKeyState('S') & 0x8000f )
g_camera.pitch(-1.0f * time_delta);
// update the view matrix representing the camera's new position/orientation
D3DXMATRIX view_matrix;
g_camera.get_view_matrix(&view_matrix);
g_device->SetTransform(D3DTS_VIEW, &view_matrix);
g_gun->update(time_delta);
// render now
g_device->Clear(0, NULL, D3DCLEAR_TARGET | D3DCLEAR_ZBUFFER, 0x00000000, 1.0f, 0);
g_device->BeginScene();
D3DXMATRIX identity_matrix;
D3DXMatrixIdentity(&identity_matrix);
g_device->SetTransform(D3DTS_WORLD, &identity_matrix);
draw_basic_scene(g_device, 1.0f);
// order important, render firework last.
g_device->SetTransform(D3DTS_WORLD, &identity_matrix);
g_gun->render();
g_device->EndScene();
g_device->Present(NULL, NULL, NULL, NULL);
return true;
}
///////////////////////////////////////////////////////////////////////////////////////////////////////
LRESULT CALLBACK wnd_proc(HWND hwnd, UINT msg, WPARAM word_param, LPARAM long_param)
{
switch(msg)
{
case WM_DESTROY:
PostQuitMessage(0);
break;
case WM_KEYDOWN:
if(word_param == VK_ESCAPE)
DestroyWindow(hwnd);
// Note: we use the message system over GetAsyncKeyState because GetAsyncKeyState was adding
// particles too fast. The message system is slower and does not add them as fast.
// This isn't the best solution, but works for illustration purposes.
if(word_param == VK_SPACE)
g_gun->add_particle();
break;
}
return DefWindowProc(hwnd, msg, word_param, long_param);
}
///////////////////////////////////////////////////////////////////////////////////////////////////////
int WINAPI WinMain(HINSTANCE inst, HINSTANCE, PSTR cmd_line, int cmd_show)
{
if(! init_d3d(inst, WIDTH, HEIGHT, true, D3DDEVTYPE_HAL, &g_device))
{
MessageBox(NULL, "init_d3d() - failed.", 0, MB_OK);
return 0;
}
if(! setup())
{
MessageBox(NULL, "Steup() - failed.", 0, MB_OK);
return 0;
}
enter_msg_loop(display);
cleanup();
g_device->Release();
return 0;
}

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