Mouse Programming with C

 

Mouse Programming is a topic which every C programmer from beginner to professional needs to have in his toolbox to have a cutting edge.It will be used almost everywhere. It will embeded in games programming to commerical valued applications. 

This tutorial is written Turbo C++ 3.0 IDE and install in folder C:\TC. I recommend to use same IDE and settings to avoid any uncompatibility.

 

Basic Funda

Before we start  programming we must first understand some principles on which mouse programming is based.

First thing you must know how to tell a mouse to do anything. In actual we do not communicate with mouse directly but through the driver provided. We use "Interrupts" to get access to this driver. Each device provide by computer has its own port and more or less we access these ports.

Each device has a unique port which is a hexadecimal value and value is designed to be machine independent enhancing portability of program.

Mouse has port 0X33 attached to it  and similarly keyboard has attach port 0X60.

We also make use of address registers. These are basically UNION of type REGS defined in "dos.h". We use two registers to communicate to a device driver one for input and one for output.

We send value to device driver through the input register and recieve information in it embedded in output register.

 

AX Register

We can access various mouse functions using different values of AX input Register and passing those values to mouse port using a interrupt.

 

The Functions are listed below - Here AX, BX, CX and DX are members of UNION REGS and more or less integers.

 

Input                   Function Performed             Returns

 

AX = 0                  Get Mouse Status           AX Value = FFFFh support is available.

                                                                   AX Value = 0 ,support is not available.

 

AX = 1                  Show Mouse Pointer                  Nothing

 

AX = 2                  Hide Mouse Pointer                   Nothing

 

AX = 3                  Mouse Position                 CX = Mouse X Coordinate

                                                                      DX = Mouse Y Coordinate

 

Ax = 3                  Mouse Button Press           BX = 0 No Key Is Pressed

                                                                     BX = 1 Left Button is Pressed

                                                                     BX = 2 Right Button is Pressed

                                                                    BX = 3 Centre Button is Pressed

 

Ax = 7                 Set Horizontal Limit                    Nothing

CX = MaxX1 

DX =MaxX2           

 

Ax = 8                 Set Vertical Limit                        Nothing

CX = MaxX1 

DX =MaxX2           

 

Detecting Mouse

Before you start your mouse program you should always check whether the mouse programming is supported or not.

If somehow mouse fails to initialise you should always make sure that either program terminates or employ a error handling approach that maybe shift to keyboard interface .

To do mouse programming you must include <dos.h>. We use a function called int86() to access "interupts".

To detect mouse we use a function name detect_mouse() which has following code -

 

 

 

Showing and Hiding Mouse

 

Now first we show mouse on screen . 

• Mouse works both in text mode and graphic mode.
• In text mode it looks like a square while in graphics mode it looks like a pointer.

 

Mouse Programming in Text Mode

 

It was produced from adding a function showmouse_text() to above code so code becomes - 

 

Mouse Programming in Graphics Mode

 

This is achieved using a function showmouse_graphics() added to above code while removing showmouse_text() from main.

 

 

Next we do realtively simple task of hiding mouse using a function hide_mouse() as shown below -

 

 

Detecting Input

 

We will now work on a important aspect of mouse programming "Detecting Clicks" i.e. Taking Inputs. 

We make use of an aditional function known as kbhit ( ). This functions returns zero till any keypress and when a key is press it returns 1.

kbhit() is used to run an infinite while loop.

For detecting mouseclicks we use a function called detect() which displays on screen the respective button clicked. Press any keyboad key to exit the loop.

#include <dos.h>

Mouse Coordinates

 

We can obtain the coordinates of the mouse using same service 3 but using different elments of the union .

This function has a prime use in games programming, application designing and GUI development. Different decisions are taken on same left button click, its the postion of click that matters.

BX element of output registers stores the X Coordinate of the postion of mouse at time of calling function.

CX element of output registers stores the Y Coordinate of the postion of mouse at time of calling function.

Now we demonstrate the use of this function by modifying detect function above to display x and y coordinates on screen when left click is pressed.

Code will be as followed -

 

 

Restricting Mouse

 

We now restrict the mouse in particular rectangle .

We create a function called restrict which takes four paramters, two cartesian points each containing one x coordinate and one y coordinate.

First point mentions the top of the rectangle while second point mention the bottom bottom point of rectangle.

This service can be quite handy in special circumstances, for eg - if you want to restrict your mouse in one particular size window in GUI or In Games Programming.

 

Final code of the tutorial -

 

#include <dos.h>

#include <graphics.h>

#include <conio.h>

#include <stdio.h>

union REGS in, out;

void restrict (int x1,int y1,int x2, int y2)

{

  in.x.ax = 7;

  in.x.cx = x1;

  in.x.dx = x2;

  int86 (0X33,&in,&out);

  in.x.ax = 8;

  in.x.cx = y1;

  in.x.dx = y2;

  int86 (0X33,&in,&out);

}

void detect_mouse ()

{

  in.x.ax = 0;

  int86 (0X33,&in,&out);

  if (out.x.ax == 0)

  printf ("\nMouse Fail To Initialize");

  else

  printf ("\nMouse Succesfully Initialize");

}

void showmouse_text ()

{

  in.x.ax = 1;

  int86 (0X33,&in,&out);

}

void showmouse_graphics ()

{

  int gdriver = DETECT, gmode, errorcode;

  initgraph(&gdriver, &gmode, "c:\\tc\\bgi");

  in.x.ax = 1;

  int86 (0X33,&in,&out);

  getch ();

  closegraph ();

}

void hide_mouse ()

{

  in.x.ax = 2;

  int86 (0X33,&in,&out);

}

void detect ()

{

  while (!kbhit () )

    {

     int x,y;

     in.x.ax = 3;

     int86 (0X33,&in,&out);

     if (out.x.bx == 1)

       {

          x = out.x.cx;

          y = out.x.dx;

          printf ("\nLeft || X - %d  Y - %d", x, y);

       }

     if (out.x.bx == 2) printf ("\nRight");

     if (out.x.bx == 3) printf ("\nMiddle");

     delay (200); // Otherwise due to quick computer response 100s 

of words will get print

    }

}

int main ()

{

  detect_mouse ();

  showmouse_text ();

  restrict (100,100,500,500); // Change values here to create 

different mouse movement space.

  detect ();

  hide_mouse ();

  getch ();

  return 0;

}

 

 

 

This was the most basic tutorial in Mouse Programming. We will be back with more advanced once very soon.

Please leave your comments, suggestions and report bugs(if any).

 

PS:- library graphics.h is incompatible with vista (working in Normal mode), because Vista doesnt support TC in fullscreen mode. 

 

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