14.3具体的粒子系统：雪、火、粒子枪
现在让我们用cParticleSystem类开始一个具体的粒子系统，为了说明用意，这些系统的设计很简单，没有用到cParticleSystem类所提供的所有灵活性。我们实现雪、火、粒子枪系统。雪系统模拟下落的雪花，火系统模拟看上去像火焰的爆炸，粒子枪系统从照相机位置向对面发射出粒子（用键盘）。
14.3.1 例子程序：雪
雪系统类定义如下：
class cSnow : public cParticleSystem
{
public:
cSnow(cBoundingBox* bounding_box, int num_particles);
virtual void reset_particle(sParticleAttribute* attr);
virtual void update(float time_delta);
};
构造函数提供一个点给边界盒结构，边界盒是粒子系统的成员。边界盒描述雪花在哪个范围内（体积范围）下落，如果雪花出了边界盒，它将被杀死并再生。这样，雪系统始终能保存有同样数量的激粒子，构造函数的实现：
cSnow::cSnow(cBoundingBox* bounding_box, int num_particles)
{
m_bounding_box = *bounding_box;
m_size = 0.25f;
m_vb_num = 2048;
m_vb_offset = 0;
m_vb_batch_num = 512;
for(int i = 0; i < num_particles; i++)
add_particle();
}
同样注意：我们指定顶点缓存的尺寸，每一批的尺寸和开始的偏移。
reset_particle方法创建一个雪花，在x、z轴随机的位置并在边界盒的范围内。设置y轴高度为边界盒的顶部。我们给雪花一个速度，以便让雪花下落时稍稍向左倾斜。雪花是白色的。
void cSnow::reset_particle(sParticleAttribute* attr)
{
attr->is_alive = true;
// get random x, z coordinate for the position of the snow flake
get_random_vector(&attr->position, &m_bounding_box.m_min, &m_bounding_box.m_max);
// no randomness for height (y-coordinate).
// Snow flake always starts at the top of bounding box.
attr->position.y = m_bounding_box.m_max.y;
// snow flakes fall downwards and slightly to the left
attr->velocity.x = get_random_float(0.0f, 1.0f) * (-3.0f);
attr->velocity.y = get_random_float(0.0f, 1.0f) * (-10.0f);
attr->velocity.z = 0.0f;
// white snow flake
attr->color = WHITE;
}
update方法更新粒子和粒子间的位置，并且测试粒子是否在系统的边界盒之外，如果它已经跳出边界盒，就再重新创建。
void cSnow::update(float time_delta)
{
for(list<sParticleAttribute>::iterator iter = m_particles.begin(); iter != m_particles.end(); iter++)
{
iter->position += iter->velocity * time_delta;
// is the point outside bounds?
if(! m_bounding_box.is_point_inside(iter->position))
// recycle dead particles, so respawn it.
reset_particle(&(*iter));
}
}
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_snow;
cCamera g_camera(AIR_CRAFT);
////////////////////////////////////////////////////////////////////////////////////////////////////
bool setup()
{
srand((unsigned int)time(NULL));
// create snow system
cBoundingBox bounding_box;
bounding_box.m_min = D3DXVECTOR3(-10.0f, -10.0f, -10.0f);
bounding_box.m_max = D3DXVECTOR3(10.0f, 10.0f, 10.0f);
g_snow = new cSnow(&bounding_box, 5000);
g_snow->init(g_device, "snowflake.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_snow;
// pass NULL for the first parameter to instruct cleanup
draw_basic_scene(NULL, 0.0f);
}
///////////////////////////////////////////////////////////////////////////////////////////////////////
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_snow->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 snow last.
g_device->SetTransform(D3DTS_WORLD, &identity_matrix);
g_snow->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);
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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