模板參數代替函數參數使用

直接看未使用模板的例子: 處理一個 a和RGB 混合的參數爲不混合rgba值, 其實爲QT中帶Premultiplied的像素轉爲普通像素,處理函數如下:

int Process(imagetype type, unsigned int* pixelhead)
{
	int R = 0, G = 0, B = 0, A = 0;
	switch (type)
	{
	case eRGBA32:
		R = 0;
		G = 1;
		B = 2;
		A = 3;
		break;
	case eARGB32:
		R = 3;
		G = 2;
		B = 1;
		A = 0;
		break;
	case eBGRA32:
		R = 2;
		G = 1;
		B = 0;
		A = 3;
		break;
	case eABGR32:
		R = 1;
		G = 2;
		B = 3;
		A = 0;
		break;
	default:
		break;
	}
	unsigned char* pixel = (unsigned char*)pixelhead;
	char a = (char)pixel[A];
	char r = (char)pixel[R];
	char g = (char)pixel[G];
	char b = (char)pixel[B];
	if (a == 0)
	{
		return 0;
	}
	pixel[R] = r * 255 / a;
	pixel[G] = g * 255 / a;
	pixel[B] = b * 255 / a;
	return 0;
}

模板的寫法有點笨拙,看似代碼量更大, 可能我寫的比較拙, 代碼如下:

#include "stdafx.h"
#include <vector>
#include <algorithm>

enum imagetype
{
	eRGBA32,
	eARGB32,
	eBGRA32,
	eABGR32
};
//這裏需要寫個基類,不然後面調用將無法new, 因爲模板參數不確定編譯不過
class BaseProcess {
public:
	virtual int Process(unsigned int * pixelhead)
	{
		return 0;
	}
};
template<imagetype T, int R, int G, int B, int A>
class DecodePremultipliedColor :public BaseProcess
{
public:
	DecodePremultipliedColor() {}
	virtual int Process(unsigned int * pixelhead)
	{
		unsigned char* pixel = (unsigned char*)pixelhead;
		char a = (char)pixel[A];
		char r = (char)pixel[R];
		char g = (char)pixel[G];
		char b = (char)pixel[B];
		if (a == 0)
		{
			return 0;
		}
		pixel[R] = r * 255 / a;
		pixel[G] = g * 255 / a;
		pixel[B] = b * 255 / a;
		return 0;
	}
};
//定義這幾種枚舉類型的實力,不然無法調用
typedef DecodePremultipliedColor<eRGBA32, 0, 1, 2, 3>  RGBA32Premultiplied;
typedef DecodePremultipliedColor<eABGR32, 3, 2, 1, 0>  ABGR32Premultiplied;
typedef DecodePremultipliedColor<eBGRA32, 2, 1, 0, 3>  BGRA32Premultiplied;
typedef DecodePremultipliedColor<eARGB32, 1, 2, 3, 0>  ARGB32Premultiplied;


int main()
{
	//模板調用
	imagetype type =eRGBA;
	BaseProcess * pProcess = 0;
	switch (type)
	{
	case eRGBA32:pProcess = new RGBA32Premultiplied(); break;
	case eARGB32:pProcess = new ARGB32Premultiplied(); break;
	case eBGRA32:pProcess = new BGRA32Premultiplied(); break;
	case eABGR32:pProcess = new ABGR32Premultiplied(); break;
	default:
		break;
	}
	unsigned int g = 0xff343433;
	pProcess->Process(&g);
	//直接函數調用
	Process(type, &g);
}

要是能直接推導第一個參數就好,可惜沒找到寫法. 另外兩種寫的代碼量竟然都是44行,不存在一個代碼量多少問題