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凹凸紋理映射

關(guān)于凹凸映射的原理請(qǐng)參閱凹凸映射（Bump Map）實(shí)現(xiàn)原理。

凹凸紋理映射是一種紋理混合方法，它可以創(chuàng)建三維物體復(fù)雜的紋理外觀表面。普通的紋理映射只能模擬比較平滑的三維物體表面，難以顯示表面高低起伏、凹凸不平的效果。凹凸紋理映射能夠通過(guò)一張表示物體表面凹凸程度的高度圖（稱為凹凸紋理），對(duì)另一張表示物體表面環(huán)境映射的紋理圖的紋理坐標(biāo)進(jìn)行相應(yīng)的干擾，經(jīng)過(guò)干擾的紋理坐標(biāo)將應(yīng)用于環(huán)境映射，從而產(chǎn)生凹凸不平的顯示效果。凹凸紋理映射通常由三張紋理映射圖組成，第一張紋理圖表示物體表面原始紋理顏色，第二張凹凸紋理圖表示物體表面凹凸的高度起伏值，用來(lái)對(duì)下一張環(huán)境紋理圖坐標(biāo)進(jìn)行干擾，第三張紋理圖表示周圍鏡面反射或漫反射光照的環(huán)境光照映射圖。凹凸紋理映射的紋理映射流程如下圖所示：

檢查硬件設(shè)備

在使用凹凸紋理映射之前，應(yīng)查詢當(dāng)前的Direct3D設(shè)備是否支持D3DTEXOPCAPS_BUMPENVMAP或D3DTEXOPCAPS_BUMPENVMAPLUMINANCE多層紋理混合，以及當(dāng)前設(shè)備是否支持3層紋理映射。

BOOL SupportsBumpMapping()
{
    D3DCAPS9 d3dCaps;
    d3dDevice->GetDeviceCaps( &d3dCaps );

    // Does this device support the two bump mapping blend operations?
    if ( 0 == d3dCaps.TextureOpCaps & ( D3DTEXOPCAPS_BUMPENVMAP | D3DTEXOPCAPS_BUMPENVMAPLUMINANCE ))
        return FALSE;

    // Does this device support up to three blending stages?
    if( d3dCaps.MaxTextureBlendStages < 3 )
        return FALSE;

    return TRUE;
}

如果當(dāng)前硬件不支持上面的任何一項(xiàng)，程序框架會(huì)自動(dòng)轉(zhuǎn)而使用參考設(shè)備。

凹凸紋理生成

Direct3D的凹凸紋理被用來(lái)表示物體表面相鄰像素的高度差，它的每個(gè)紋理元素由表示水平相鄰像素高度差的D_u、表示垂直相鄰像素高度差的D_v以及表示該點(diǎn)亮度的L組成（某些凹凸紋理像素格式可以不包含L）。下表列出了Direct3D支持的凹凸紋理像素格式：

通常情況下，可以載入一張表示物體表面圖像高度的紋理圖，通過(guò)計(jì)算高度圖水平相鄰和垂直相鄰元素的高度差來(lái)生成凹凸紋理，也可以通過(guò)程序生成凹凸紋理，這里根據(jù)紋理圖來(lái)生成凹凸紋理，代碼如下：

//--------------------------------------------------------------------------------------
// Create bump texture from height map texture.
//--------------------------------------------------------------------------------------
HRESULT CreateBumpTexture(IDirect3DDevice9* device)
{
	HRESULT hr;

	D3DSURFACE_DESC surface_desc;
	g_height_map_texture->GetLevelDesc(0, &surface_desc);

	V_RETURN(device->CreateTexture(surface_desc.Width, surface_desc.Height, 1, 0, D3DFMT_X8L8V8U8, D3DPOOL_MANAGED,
								   &g_bump_map_texture, NULL));

	D3DLOCKED_RECT locked_rect;
	g_height_map_texture->LockRect(0, &locked_rect, NULL, 0);

	DWORD src_pitch   = (DWORD) locked_rect.Pitch;
	BYTE* src_row_top = (BYTE*) locked_rect.pBits;
	BYTE* src_row_cur = src_row_top;
	BYTE* src_row_bot = src_row_top + src_pitch * (surface_desc.Height - 1);

	g_bump_map_texture->LockRect(0, &locked_rect, NULL, 0);

	DWORD dest_pitch   = (DWORD) locked_rect.Pitch;
	BYTE* dest_row_top = (BYTE*) locked_rect.pBits;
	BYTE* dest_row_cur = dest_row_top;

	// iterate through all lines
	for(DWORD y = 0; y < surface_desc.Height; y++)
	{
		BYTE* src_pixel_cur;
		BYTE* src_pixel_up;
		BYTE* src_pixel_below;		
		BYTE* dest_pixel;

		src_pixel_cur = src_row_cur;

		if(y == 0)
			src_pixel_up = src_row_bot;
		else
			src_pixel_up = src_row_cur - src_pitch;

		if(y == surface_desc.Height - 1)
			src_pixel_below = src_row_top;
		else
			src_pixel_below = src_row_cur + src_pitch;

		dest_pixel = dest_row_cur;

		// iterate through all columns in current line
		for(DWORD x = 0; x < surface_desc.Width; x++)
		{
			BYTE src_pixel_left, src_pixel_right;

			if(x == 0)
				src_pixel_left = *(src_row_cur + (surface_desc.Width - 4));
			else
				src_pixel_left = *(src_pixel_cur - 4);

			if(x == surface_desc.Width - 1)
				src_pixel_right = *src_row_cur;
			else
				src_pixel_right = *(src_pixel_cur + 4);

			BYTE du = BYTE(src_pixel_left - src_pixel_right);
			BYTE dv = BYTE(src_pixel_up   - src_pixel_below);

			// the luminance bump value
			BYTE u_lumi = (*src_pixel_cur > 1) ? 63 : 127;

			*dest_pixel++ = du;
			*dest_pixel++ = dv;
			*dest_pixel++ = u_lumi;
			*dest_pixel++ = 0;

			// move one pixel to the right
			src_pixel_cur   += 4;
			src_pixel_up     += 4;
			src_pixel_below += 4;			
		}

		// move to the next line
		src_row_cur  += src_pitch;
		dest_row_cur += dest_pitch;
	}

	g_bump_map_texture->UnlockRect(0);
	g_height_map_texture->UnlockRect(0);

	return S_OK;
}

凹凸紋理設(shè)置

凹凸紋理映射通常使用3層紋理：物體原始紋理、由原始紋理高度圖生成的凹凸紋理、環(huán)境紋理，對(duì)應(yīng)于多層紋理混合的0、1、2層。指定當(dāng)前紋理層狀態(tài)為D3DTOP_BUMPENVMAP或D3DTOP_BUMPENVMAPLUMINANCE可設(shè)置當(dāng)前紋理層為凹凸紋理，例如：

pd3dDevice->SetTexture(1, g_bump_map_texture);
pd3dDevice->SetTextureStageState(1, D3DTSS_COLOROP,		   D3DTOP_BUMPENVMAP);

或

pd3dDevice->SetTexture(1, g_bump_map_texture);
pd3dDevice->SetTextureStageState(1, D3DTSS_COLOROP,		   D3DTOP_BUMPENVMAPLUMINANCE);

紋理狀態(tài)D3DTOP_BUMPENVMAP和D3DTOP_BUMPENVMAPLUMINANCE表示兩種不同的凹凸紋理映射方法。紋理狀態(tài)D3DTOP_BUMPENVMAPLUMINANCE表示在凹凸紋理中包含凹凸紋理亮度值L，L將與下一紋理層的紋理顏色相乘作為最后輸出的紋理顏色。紋理狀態(tài)D3DTOP_BUMPENVMAP默認(rèn)亮度值L為1，即不改變下一紋理層的紋理顏色。

這里分別使用了3層紋理貼圖，如下所示：

原始紋理

原始紋理高度圖

環(huán)境紋理貼圖

Direct3D可設(shè)置凹凸紋理矩陣，對(duì)凹凸紋理中的每個(gè)紋理元素值（D_v、D_u，即對(duì)于下一紋理層中的每個(gè)紋理坐標(biāo)的擾動(dòng)值）進(jìn)行坐標(biāo)變換：

D_u' = D_u * M₀₀ + D_v * M₁₀

D_v' = D_v * M₀₁ + D_v * M₁₁

凹凸紋理的每個(gè)紋理元素D_v、D_u與一個(gè)2 x 2的凹凸矩陣相乘，其結(jié)果D_v、D_u對(duì)下一紋理層中的每個(gè)紋理元素的紋理坐標(biāo)產(chǎn)生該數(shù)值代表的坐標(biāo)擾動(dòng)。2 x 2的凹凸矩陣值可由函數(shù)IDirect3DDevice9::SetTextureStageState()設(shè)置，將它的第一個(gè)參數(shù)設(shè)置為紋理層序號(hào)，第二個(gè)參數(shù)設(shè)置為D3DTSS_BUMPENVMAT00或D3DTSS_BUMPENVMAT01或D3DTSS_BUMPENVMAT10或D3DTSS_BUMPENVMAT11，分別表示凹凸矩陣的4個(gè)矩陣元素，第三個(gè)參數(shù)設(shè)置為該矩陣元素的值。紋理坐標(biāo)擾動(dòng)D_v、D_u或D_v'、D_u'的范圍介于-1 ~ +1之間。

如果使用D3DTOP_BUMPENVMAPLUMINANCE計(jì)算凹凸紋理，Direct3D將使用下列方程計(jì)算凹凸紋理的亮度值L'（L'為0~255的整數(shù)，它將被用來(lái)與下一紋理層的顏色相乘，作為最后輸出的紋理顏色值）。

L' = L * S + O

其中，L為凹凸紋理元素中的亮度L值，比例系數(shù)S和偏移系數(shù)O可改變最終的亮度值。S和O可由函數(shù)IDirect3DDevice9::SetTexureStageState()設(shè)置，將它的第一個(gè)參數(shù)設(shè)置為紋理層序號(hào)，第二個(gè)參數(shù)設(shè)置為D3DTSS_BUMPENVLSCALE或D3DTSS_BUMPENVLOFFSET，分別表示凹凸紋理映射的比例系數(shù)S和偏移系數(shù)O，將第三個(gè)參數(shù)設(shè)置為相應(yīng)的系數(shù)值。

設(shè)置凹凸紋理狀態(tài)的代碼如下所示：

// set texture color blend method for stage 0 (base texture)

pd3dDevice->SetTextureStageState(0, D3DTSS_COLORARG1, D3DTA_TEXTURE);
pd3dDevice->SetTextureStageState(0, D3DTSS_COLOROP, D3DTOP_SELECTARG1);

pd3dDevice->SetSamplerState(0, D3DSAMP_MAGFILTER, D3DTEXF_LINEAR);
pd3dDevice->SetSamplerState(0, D3DSAMP_MINFILTER, D3DTEXF_LINEAR);

// set texture color blend method for stage 1 (bump map texture)

pd3dDevice->SetTexture(1, g_bump_map_texture);

pd3dDevice->SetTextureStageState(1, D3DTSS_TEXCOORDINDEX, 0);

pd3dDevice->SetTextureStageState(1, D3DTSS_COLOROP, D3DTOP_BUMPENVMAPLUMINANCE);
pd3dDevice->SetTextureStageState(1, D3DTSS_COLORARG1, D3DTA_TEXTURE);
pd3dDevice->SetTextureStageState(1, D3DTSS_COLORARG2, D3DTA_CURRENT);

pd3dDevice->SetTextureStageState(1, D3DTSS_BUMPENVMAT00, F2DW(0.8f));
pd3dDevice->SetTextureStageState(1, D3DTSS_BUMPENVMAT01, F2DW(0.0f));
pd3dDevice->SetTextureStageState(1, D3DTSS_BUMPENVMAT10, F2DW(0.0f));
pd3dDevice->SetTextureStageState(1, D3DTSS_BUMPENVMAT11, F2DW(0.8f));

pd3dDevice->SetTextureStageState(1, D3DTSS_BUMPENVLSCALE, F2DW(4.0f));
pd3dDevice->SetTextureStageState(1, D3DTSS_BUMPENVLOFFSET, F2DW(0.0f));

pd3dDevice->SetSamplerState(1, D3DSAMP_MAGFILTER, D3DTEXF_LINEAR);
pd3dDevice->SetSamplerState(1, D3DSAMP_MINFILTER, D3DTEXF_LINEAR);

// set texture color blend method for stage 2 (environment map texture)

D3DXMATRIX mat;

mat._11 = 0.5f; mat._12 = 0.0f; mat._13 = 0.0f; mat._14 = 0.0f;
mat._21 = 0.0f; mat._22 = -0.5f; mat._23 = 0.0f; mat._24 = 0.0f;
mat._31 = 0.0f; mat._32 = 0.0f; mat._33 = 1.0f; mat._34 = 0.0f;
mat._41 = 0.5f; mat._42 = 0.5f; mat._43 = 0.0f; mat._44 = 1.0f;

pd3dDevice->SetTransform(D3DTS_TEXTURE2, &mat);

pd3dDevice->SetTexture(2, g_env_map_texture);

pd3dDevice->SetTextureStageState(2, D3DTSS_TEXTURETRANSFORMFLAGS, D3DTTFF_COUNT2);
pd3dDevice->SetTextureStageState(2, D3DTSS_TEXCOORDINDEX, D3DTSS_TCI_SPHEREMAP);
pd3dDevice->SetTextureStageState(2, D3DTSS_COLORARG1, D3DTA_TEXTURE);
pd3dDevice->SetTextureStageState(2, D3DTSS_COLORARG2, D3DTA_CURRENT);
pd3dDevice->SetTextureStageState(2, D3DTSS_COLOROP, D3DTOP_ADD);

pd3dDevice->SetSamplerState(2, D3DSAMP_MAGFILTER, D3DTEXF_LINEAR);
pd3dDevice->SetSamplerState(2, D3DSAMP_MINFILTER, D3DTEXF_LINEAR);

原始紋理圖

經(jīng)過(guò)凹凸紋理映射后

主程序：

下載示例工程