OpenCv

Accessing each element in a matrix:

for( int i=0; i<rows; i++ ) {
		for( int j=0; j<cols; j++ ) { 
			result.at<float>(i, j) = src.at<float>(i+disparity, j+disparity);
			cout << result.at<float>(i, j) << " ";
		}
		cout << endl;
	}

Threshold:
Flags:

  • THRESH_BINARY

    \texttt{dst} (x,y) =  \fork{\texttt{maxval}}{if $\texttt{src}(x,y) > \texttt{thresh}$}{0}{otherwise}

  • THRESH_BINARY_INV

    \texttt{dst} (x,y) =  \fork{0}{if $\texttt{src}(x,y) > \texttt{thresh}$}{\texttt{maxval}}{otherwise}

  • THRESH_TRUNC

    \texttt{dst} (x,y) =  \fork{\texttt{threshold}}{if $\texttt{src}(x,y) > \texttt{thresh}$}{\texttt{src}(x,y)}{otherwise}

  • THRESH_TOZERO

    \texttt{dst} (x,y) =  \fork{\texttt{src}(x,y)}{if $\texttt{src}(x,y) > \texttt{thresh}$}{0}{otherwise}

  • THRESH_TOZERO_INV

    \texttt{dst} (x,y) =  \fork{0}{if $\texttt{src}(x,y) > \texttt{thresh}$}{\texttt{src}(x,y)}{otherwise}

API:

double threshold(InputArray src, OutputArray dst, double thresh, double maxval, int type)
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Virtual Function in C++

I think it would be the best if we run an example first, so let’s do that:

#include <iostream>
#include <string>

using namespace std;

class Base
{
public:
    string nonVirtualMethod() {
        return "Base: non virtual method.";
    }
    virtual string virtualMethod() {
        return "Base: virtual method.";
    }
};

class Derived : public Base
{
public:
    string nonVirtualMethod() {
        return "Derived: non virtual method.";
    }
    string virtualMethod() {
        return "Derived: virtual method.";
    }
};

int main()
{
    Derived *derivedObject = new Derived();
    cout << "Derived::non-virtual(): -> " << derivedObject->nonVirtualMethod() << endl;
    cout << "Derived::virtual(): -> " << derivedObject->virtualMethod() << endl;
    cout << endl;

    Base *baseObject = new Derived();
    cout << "Base::non-virtual() -> " << baseObject->nonVirtualMethod() << endl;
    cout << "Base::virtual() -> " << baseObject->virtualMethod() << endl;
    cout << endl;

    return 0;
}

As we can see from the example, when a method is declared “virtual”, the method of the defined class is used. Let’s further dive into this.

Base *baseObject = new Derived();

 

Non-Virtual Function
Without the virtual keyword added, methods look for their definition in the declared class. When calling baseObject->nonVirtualMethod(), the compiler looks at the type of the baseObject (which is Base) and then runs function definition in Base class.
So, non-virtual functions looks at: Base *baseObject => Base

Base *baseObject;
baseObject->nonVirtualMethod(); //Calling Base::nonVirtualMethod

 

Virtual Function
On the other hand, because baseObject is instantiated as Derived object (and we most often want to use the derived method instead), when we call baseObject->virtualMethod(), it checks out what the type baseObject is really pointing to (baseObject = new Derived()), then runs the function definition from Derive class.

Virtual function looks at: baseObject = new Derived() => Derive

baseObject = new Derived();
baseObject->virtualMethod(); //Calling Derived::virtualMethod

Hope this kinda help.

What is C-style Array?

A C-Style array is just a “naked” array – that is, an array that’s not wrapped in a class, like this:

char[] array = {'a', 'b', 'c', ''};

Or a pointer if you use it as an array:

Thing* t = new Thing[size];
t[someindex].dosomething();

And a “C++ style array” (the unofficial but popular term) is just what you mention – a wrapper class likestd::vector (or std::array). That’s just a wrapper class (that’s really a C-style array underneath) that provides handy capabilities like bounds checking and size information.

Extracted from: Seth Carnegie’s Solution on StackOverflow

DirectX Project Setup in Visual Studio 2013

Before following the step, make sure you have already included $(DXSDK_DIR) macro in include and Lib under VC++ directories. (Only need to be done once. See how.) The steps below, however, must be performed every time a new DirectX project is created.

Step 1: Right click on your project -> Select Properties
10

Step 2: On the left hand panel, select Configuration Properties -> Linker -> Input. Make sure “All Configurations” is selected in the drop down menu.
11

Step 3: add and type in d3dx10.lib;d3dx10.lib; in Additional Dependencies as shown in the figure below:
12

Step 4: Run a sample DirectX cpp to make sure it works.

/***************************************
 DirectXTutorial.com
 Lesson 1: Create a blue window

 File name: BlueWindow.cpp
 Description:
	This program creates a window with
	blue background that does nothing.
 ***************************************/

#include <windows.h>
#include <windowsx.h>
#include <d3d9.h>

#pragma comment (lib, "d3d9.lib")

LPDIRECT3D9 d3d;
LPDIRECT3DDEVICE9 d3ddev;

void initD3D(HWND hWnd);
void render_frame(void);
void cleanD3D(void);

LRESULT CALLBACK WindowProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam);

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
	HWND hWnd;
	WNDCLASSEX wc;

	ZeroMemory(&wc, sizeof(WNDCLASSEX));

	wc.cbSize = sizeof(WNDCLASSEX);
	wc.style = CS_HREDRAW | CS_VREDRAW;
	wc.lpfnWndProc = WindowProc;
	wc.hInstance = hInstance;
	wc.hCursor = LoadCursor(NULL, IDC_ARROW);
	wc.hbrBackground = (HBRUSH)COLOR_WINDOW;
	wc.lpszClassName = "WindowClass";

	RegisterClassEx(&wc);

	hWnd = CreateWindowEx(NULL, "WindowClass", "Blue Window Program", WS_OVERLAPPEDWINDOW,
		300, 300, 800, 600, NULL, NULL, hInstance, NULL);

	ShowWindow(hWnd, nCmdShow);

	initD3D(hWnd);

	MSG msg;
	while (TRUE) {
		while (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE)) {
			TranslateMessage(&msg);
			DispatchMessage(&msg);
		}
		if (msg.message == WM_QUIT)
			break;
		render_frame();
	}
	cleanD3D();
	return msg.wParam;
}

LRESULT CALLBACK WindowProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
	switch (message)
	{
		case WM_DESTROY:
		{
		   PostQuitMessage(0);
		   return 0;
		} break;
	}
	return DefWindowProc(hWnd, message, wParam, lParam);
}

void initD3D(HWND hWnd)
{
	d3d = Direct3DCreate9(D3D_SDK_VERSION);

	D3DPRESENT_PARAMETERS d3dpp;

	ZeroMemory(&d3dpp, sizeof(d3dpp));
	d3dpp.Windowed = TRUE;
	d3dpp.SwapEffect = D3DSWAPEFFECT_DISCARD;
	d3dpp.hDeviceWindow = hWnd;

	d3d->CreateDevice(D3DADAPTER_DEFAULT, D3DDEVTYPE_HAL, hWnd, D3DCREATE_SOFTWARE_VERTEXPROCESSING,
		&d3dpp, &d3ddev);
}

void render_frame(void)
{
	d3ddev->Clear(0, NULL, D3DCLEAR_TARGET, D3DCOLOR_XRGB(0, 4, 100), 1.0f, 0);
	d3ddev->BeginScene();
	d3ddev->EndScene();
	d3ddev->Present(NULL, NULL, NULL, NULL);
}

void cleanD3D(void)
{
	d3ddev->Release();
	d3d->Release();
}

Sources: