材質(zhì)alpha
頂點(diǎn)alpha是沒有使用光照和材質(zhì)的情況，如果對(duì)場(chǎng)景內(nèi)的物體添加光照和材質(zhì)而沒有添加紋理時(shí)，頂點(diǎn)alpha值取決于材質(zhì)屬性中漫反射顏色的alpha系數(shù)和燈光顏色中的alpha系數(shù)，頂點(diǎn)alpha值是根據(jù)光照計(jì)算得到的。頂點(diǎn)光照計(jì)算是分別針對(duì)紅、綠、藍(lán)和alpha進(jìn)行的，其中alpha光照計(jì)算的結(jié)果就是頂點(diǎn)的alpha值。有了頂點(diǎn)的alpha值就可根據(jù)著色模式計(jì)算出每個(gè)像素的alpha值，第一個(gè)示例程序就是材質(zhì)alpha的例子。
紋理alpha
當(dāng)對(duì)物體表面使用了紋理之后，像素的alpha值就是紋理alpha混合之后的值，所以這又取決于紋理的alpha混合方法，紋理alpha混合方法決定了紋理alpha混合之后的alpha值是取自材質(zhì)，還是取自紋理，或者取自二者的某種運(yùn)算。像素alpha值的具體計(jì)算過(guò)程是這樣的，首先得到頂點(diǎn)alpha值，頂點(diǎn)alpha值可能是直接指定的，也可能是光照計(jì)算得到，然后根據(jù)著色模式對(duì)頂點(diǎn)alpha值進(jìn)行插值，得到的結(jié)果再根據(jù)紋理alpha混合方法和紋理采樣得到的alpha值進(jìn)行指定的運(yùn)算，得到最終每個(gè)像素的alpha值。
示例程序中將一幅紋理應(yīng)用到一個(gè)矩形表面，其中紋理alpha混合的設(shè)置如下：
g_device->SetTextureStageState(0, D3DTSS_ALPHAOP, D3DTOP_MODULATE);
g_device->SetTextureStageState(0, D3DTSS_ALPHAARG1, D3DTA_TEXTURE);
g_device->SetTextureStageState(0, D3DTSS_ALPHAARG2, D3DTA_DIFFUSE);
- D3DTOP_MODULATE
- Multiply the components of the arguments.
SRGBA = Arg1 x
Arg2
在示例程序中將矩形4個(gè)頂點(diǎn)的顏色值設(shè)置為0xFFFFFFFF，其alpha成分設(shè)置為ff，即alpha值為1.0f，所以紋理alpha混合的最終結(jié)果就是取紋理的alpha值。
sCustomVertex vertices[] =
{
{ -3, -3, 0.0f, 0xffffffff, 0.0f, 1.0f},
{ -3, 3, 0.0f, 0xffffffff, 0.0f, 0.0f},
{ 3, -3, 0.0f, 0xffffffff, 1.0f, 1.0f},
{ 3, 3, 0.0f, 0xffffffff, 1.0f, 0.0f}
}
示例程序在一個(gè)矩形表面貼了一顆樹的紋理，在樹的紋理中，沒有樹葉和樹枝的地方alpha值為0，即完全透明；有樹葉和樹枝的地方alpha值為1，即完全不透明。所以通過(guò)alpha混合后，渲染的結(jié)果就像是一棵真的樹。
按下數(shù)字鍵"1"，啟用紋理alpha混合。
按下數(shù)字鍵"0"，禁用紋理alpha混合。
將頂點(diǎn)alpha由ff改為88后啟用紋理混合的效果，可以看出紋理的顏色變暗了。
sCustomVertex vertices[] =
{
{ -3, -3, 0.0f, 0x88ffffff, 0.0f, 1.0f},
{ -3, 3, 0.0f, 0x88ffffff, 0.0f, 0.0f},
{ 3, -3, 0.0f, 0x88ffffff, 1.0f, 1.0f},
{ 3, 3, 0.0f, 0x88ffffff, 1.0f, 0.0f}
};
源程序：
#include <d3dx9.h>
#pragma warning(disable : 4127) // disable warning: conditional expression is constant
#define CLASS_NAME "GameApp"
#define release_com(p) do { if(p) { (p)->Release(); (p) = NULL; } } while(0)
typedef unsigned char uchar;
IDirect3D9* g_d3d;
IDirect3DDevice9* g_device;
IDirect3DVertexBuffer9* g_vertex_buffer;
IDirect3DTexture9* g_texture;
struct sCustomVertex
{
float x, y, z;
DWORD color;
float u, v;
};
#define D3DFVF_CUSTOM_VERTEX (D3DFVF_XYZ | D3DFVF_DIFFUSE | D3DFVF_TEX1)
void setup_matrices()
{
// setup world matrix
D3DXMATRIX mat_world;
D3DXMatrixIdentity(&mat_world);
g_device->SetTransform(D3DTS_WORLD, &mat_world);
// setup view matrix
D3DXVECTOR3 eye(0.0f, 0.0f, -10.0f);
D3DXVECTOR3 at(0.0f, 0.0f, 0.0f);
D3DXVECTOR3 up(0.0f, 1.0f, 0.0f);
D3DXMATRIX mat_view;
D3DXMatrixLookAtLH(&mat_view, &eye, &at, &up);
g_device->SetTransform(D3DTS_VIEW, &mat_view);
// setup projection matrix
D3DXMATRIX mat_proj;
D3DXMatrixPerspectiveFovLH(&mat_proj, D3DX_PI/4, 1.0f, 1.0f, 100.0f);
g_device->SetTransform(D3DTS_PROJECTION, &mat_proj);
}
bool init_vb()
{
if(FAILED(D3DXCreateTextureFromFile(g_device, "tree.tga", &g_texture)))
{
MessageBox(NULL, "Can not load texture file tree.tga!", "ERROR", MB_OK);
return false;
}
sCustomVertex vertices[] =
{
{ -3, -3, 0.0f, 0xffffffff, 0.0f, 1.0f},
{ -3, 3, 0.0f, 0xffffffff, 0.0f, 0.0f},
{ 3, -3, 0.0f, 0xffffffff, 1.0f, 1.0f},
{ 3, 3, 0.0f, 0xffffffff, 1.0f, 0.0f}
/*
{ -3, -3, 0.0f, 0x88ffffff, 0.0f, 1.0f},
{ -3, 3, 0.0f, 0x88ffffff, 0.0f, 0.0f},
{ 3, -3, 0.0f, 0x88ffffff, 1.0f, 1.0f},
{ 3, 3, 0.0f, 0x88ffffff, 1.0f, 0.0f}
*/
};
g_device->CreateVertexBuffer(sizeof(vertices), 0, D3DFVF_CUSTOM_VERTEX, D3DPOOL_DEFAULT, &g_vertex_buffer, NULL);
void* ptr;
g_vertex_buffer->Lock(0, 0, &ptr, 0);
memcpy(ptr, vertices, sizeof(vertices));
g_vertex_buffer->Unlock();
return true;
}
bool init_d3d(HWND hwnd)
{
g_d3d = Direct3DCreate9(D3D_SDK_VERSION);
if(g_d3d == NULL)
return false;
D3DPRESENT_PARAMETERS d3dpp;
ZeroMemory(&d3dpp, sizeof(d3dpp));
d3dpp.Windowed = TRUE;
d3dpp.SwapEffect = D3DSWAPEFFECT_DISCARD;
d3dpp.BackBufferFormat = D3DFMT_UNKNOWN;
if(FAILED(g_d3d->CreateDevice(D3DADAPTER_DEFAULT, D3DDEVTYPE_HAL, hwnd, D3DCREATE_SOFTWARE_VERTEXPROCESSING,
&d3dpp, &g_device)))
{
return false;
}
if(! init_vb())
return false;
setup_matrices();
g_device->SetRenderState(D3DRS_LIGHTING, FALSE);
g_device->SetRenderState(D3DRS_ALPHABLENDENABLE, TRUE);
g_device->SetRenderState(D3DRS_SRCBLEND, D3DBLEND_SRCALPHA);
g_device->SetRenderState(D3DRS_DESTBLEND, D3DBLEND_INVSRCALPHA);
g_device->SetTextureStageState(0, D3DTSS_COLOROP, D3DTOP_SELECTARG1);
g_device->SetTextureStageState(0, D3DTSS_COLORARG1, D3DTA_TEXTURE);
g_device->SetTextureStageState(0, D3DTSS_ALPHAOP, D3DTOP_MODULATE);
g_device->SetTextureStageState(0, D3DTSS_ALPHAARG1, D3DTA_TEXTURE);
g_device->SetTextureStageState(0, D3DTSS_ALPHAARG2, D3DTA_DIFFUSE);
return true;
}
void cleanup()
{
release_com(g_vertex_buffer);
release_com(g_texture);
release_com(g_device);
release_com(g_d3d);
}
void render()
{
g_device->Clear(0, NULL, D3DCLEAR_TARGET, D3DCOLOR_XRGB(55, 5, 5), 1.0f, 0);
g_device->BeginScene();
g_device->SetTexture(0, g_texture);
g_device->SetStreamSource(0, g_vertex_buffer, 0, sizeof(sCustomVertex));
g_device->SetFVF(D3DFVF_CUSTOM_VERTEX);
g_device->DrawPrimitive(D3DPT_TRIANGLESTRIP, 0, 2);
g_device->EndScene();
g_device->Present(NULL, NULL, NULL, NULL);
}
LRESULT WINAPI WinProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
switch(msg)
{
case WM_KEYDOWN:
switch(wParam)
{
case VK_ESCAPE:
DestroyWindow(hwnd);
break;
case 48: // press key "0", disable alpha blend.
g_device->SetRenderState(D3DRS_ALPHABLENDENABLE, FALSE);
break;
case 49: // press key "1", enable alpha blend.
g_device->SetRenderState(D3DRS_ALPHABLENDENABLE, TRUE);
break;
}
break;
case WM_DESTROY:
PostQuitMessage(0);
return 0;
}
return DefWindowProc(hwnd, msg, wParam, lParam);
}
int WINAPI WinMain(HINSTANCE inst, HINSTANCE, LPSTR, INT)
{
WNDCLASSEX wc;
wc.cbSize = sizeof(WNDCLASSEX);
wc.style = CS_CLASSDC;
wc.lpfnWndProc = WinProc;
wc.cbClsExtra = 0;
wc.cbWndExtra = 0;
wc.hInstance = inst;
wc.hIcon = NULL;
wc.hCursor = NULL;
wc.hbrBackground = NULL;
wc.lpszMenuName = NULL;
wc.lpszClassName = CLASS_NAME;
wc.hIconSm = NULL;
if(! RegisterClassEx(&wc))
return -1;
HWND hwnd = CreateWindow(CLASS_NAME, "Direct3D App", WS_OVERLAPPEDWINDOW, 200, 100, 600, 500,
NULL, NULL, wc.hInstance, NULL);
if(hwnd == NULL)
return -1;
if(init_d3d(hwnd))
{
ShowWindow(hwnd, SW_SHOWDEFAULT);
UpdateWindow(hwnd);
MSG msg;
ZeroMemory(&msg, sizeof(msg));
while(msg.message != WM_QUIT)
{
if(PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
render();
Sleep(10);
}
}
cleanup();
UnregisterClass(CLASS_NAME, wc.hInstance);
return 0;
}
下載示例工程