How to draw an opaque, screen-sized, black rectangle?

How to draw an opaque, screen-sized, black rectangle?

cameron

Member #8,219

January 2007

Hey all,

I have a game in development and to add a more professional touch I want it so when certain messages appear to the player, and when the user pauses the game, etc, the following should happen:

1. a black rectangle at 50% opacity should fill the entire screen
2. text should be displayed at 100% opacity on top of said rectangle
3. the game should pause until a key [P] is pressed

I have #3 done as the following:

        if (key[KEY_P]) { // pause 
                        if (pause == false) pause = true; rest(100);
                        //if (pause) pause = false; rest(100)
                        }
        
        if (pause) { 
                   while (!key[KEY_P]) {
                                   // paused!
                                   }
                   pause = false; rest(100);
                   }

how would i go about drawing a large black opaque rectangle though - i don't know how to do opacity in allegro!

thanks for your help, cameron

Kauhiz

Member #4,798

July 2004

Actually, you apparently don't want an opaque rectangle - opaque means 100% opacity . What you want is transcluency. Just look in the manual. A word of warning; trancluency is slow if you're using plain allegro! Since you're pausing the game you might get away with only doing the transcluent blit once, though, since the screen won't change.

---
It's Ridge Racer! RIIIIIDGE RAAAAACER!

gnolam

Member #2,030

March 2002

To be specific, look up

set_trans_blender()
drawing_mode()

BTW, the rest()s in your code concern me. You're not doing your game timing with rest(), are you?

--
Move to the Democratic People's Republic of Vivendi Universal (formerly known as Sweden) - officially democracy- and privacy-free since 2008-06-18!

piccolo

Member #3,163

January 2003

try messin around with this stuff use a square spite or drawRectangle

 /* Some one time initialisation code. */
      COLOR_MAP global_trans_table;
      create_trans_table(&global_trans_table, my_palette,
       128, 128, 128, NULL);
      ...
      if (get_color_depth() == 8)
   color_map = &global_trans_table;
      else
   set_trans_blender(128, 128, 128, 128);



      draw_trans_sprite(buffer, ghost_sprite, x, y);

makeacol32
Converts an RGBA color into a 32-bit display pixel format.
Description
int makeacol32(int r, int g, int b, int a);
drawRectangle

1// draw a rectangle
2// since we use it three times in the editor, it would be nice to have
3// a function for it.
4void drawRectangle(BITMAP *bmp,int x, int y, int w,int h,int color, int style, int bgcolor)
5{
w--;
h--;
if (style==0)
{
  vline(bmp,x,y,y+h,color);
  vline(bmp,x+w,y,y+h,color);
  hline(bmp,x,y,x+w,color);
  hline(bmp,x,y+h,x+w,color);
}
if (style==1)
{
  rectfill(bmp,x,y,x+w,y+h,bgcolor);
  vline(bmp,x,y,y+h,color);
  vline(bmp,x+w,y,y+h,color);
  hline(bmp,x,y,x+w,color);
  hline(bmp,x,y+h,x+w,color);
}
23 
24 
// this is for our dialog. This draws a box with rounded corners.
if (style==2)
{                  
  arc(bmp,x+10,y+10,itofix(64),itofix(128),10,255);
  arc(bmp,x+10,y+h-10,itofix(128),itofix(192),10,255);
  arc(bmp,x+w-10,y+10,itofix(0),itofix(64),10,255);
  arc(bmp,x+w-10,y+h-10,itofix(192),itofix(256),10,255);
32 
33 
  hline(bmp,x+10,y,x+w-10,255);
  hline(bmp,x+10,y+h,x+w-10,255);
  vline(bmp,x,y+10,y+h-10,255);
  vline(bmp,x+w,y+10,y+h-10,255);

  floodfill(bmp,x+w/2,y+h/2,255);
40 
  arc(bmp,x+10,y+10,itofix(64),itofix(128),8,bgcolor);
  arc(bmp,x+10,y+h-10,itofix(128),itofix(192),8,bgcolor);
  arc(bmp,x+w-10,y+10,itofix(0),itofix(64),8,bgcolor);
  arc(bmp,x+w-10,y+h-10,itofix(192),itofix(256),8,bgcolor);
45 
46 
  hline(bmp,x+10,y+2,x+w-10,bgcolor);
  hline(bmp,x+10,y+h-2,x+w-10,bgcolor);
  vline(bmp,x+2,y+10,y+h-10,bgcolor);
  vline(bmp,x+w-2,y+10,y+h-10,bgcolor);
51 
  floodfill(bmp,x+w/2,y+h/2,bgcolor);
}
54}

wow
-------------------------------
i am who you are not am i

gnolam

Member #2,030

March 2002

piccolo strikes again! Seriously, that's the clumsiest way to draw rectangles in Allegro that I've ever seen.

--
Move to the Democratic People's Republic of Vivendi Universal (formerly known as Sweden) - officially democracy- and privacy-free since 2008-06-18!

cameron

Member #8,219

January 2007

gnolam, yes, i am. this is my second game ever. (first was pong) i have a lot to learn.

piccolo i am confused as to how to use that.. (and why not just use rectfill() )

and thanks for all the help guys.

gnolam

Member #2,030

March 2002

Allegro FAQ to the rescue!

Implement that. Please. Friends don't let friends do rest() timing.

--
Move to the Democratic People's Republic of Vivendi Universal (formerly known as Sweden) - officially democracy- and privacy-free since 2008-06-18!

Kikaru

Member #7,616

August 2006

Exactly! Timed game loops saved two of my best games from the recycle bin!

cameron

Member #8,219

January 2007

gnolam, i have implemented the counter as you suggested, still not sure what to do in relation to the black-transparency screen problem. i looked at the docu, i guess i just don't know enough about allegro and it's functions to mess with it yet.

thanks guys. oh, and what is the primary benefits to doing this counter over rest()?

gnolam

Member #2,030

March 2002

Quote:

Well, what's the problem?

Quote:

thanks guys. oh, and what is the primary benefits to doing this counter over rest()?

The timer-based method actually works. rest() will, at best, work on one computer - yours.

--
Move to the Democratic People's Republic of Vivendi Universal (formerly known as Sweden) - officially democracy- and privacy-free since 2008-06-18!

Kikaru

Member #7,616

August 2006

Rest works like this:

//loop took 5 milliseconds
rest(20) //rest for 20 milliseconds
//total time: 25 milliseconds

Timed Loops work like this:

//loop took 5 milliseconds
while (timer < loop_start+20){}; //waits until it was been at least 20 
//milliseconds since the START of the loop
//total time: 20 milliseconds

LennyLen

Member #5,313

December 2004

Quote:

//loop took 5 milliseconds
rest(20) //rest for 20 milliseconds
//total time: 25 milliseconds

That's providing of course the loop takes 5 miliseconds, which it won't on all machines. Which is why you don't use rest() for timing.

cameron

Member #8,219

January 2007

thanks for the explanation. I'm now rest()-free.

il update you on the black screen thing tomorrow.. i'm off to bed.

Evert

Member #794

November 2000

Quote:

1. a black rectangle at 50% opacity should fill the entire screen

An old-school (and cheap) way of getting this effect is to use dithering: turn alternate pixels black in a checkerboard pattern. If your resolution is high enough, the difference is not noticable unless you look closely. You could even make this an option.

piccolo

Member #3,163

January 2003

that can be done something like this.

1 
2void do_trans(BITMAP *dest){
  int color = makecol(0,0,0);
  int fourth_width = dest->w/4;
  for(int y = 0; y <= dest->h; ++y) {
      unsigned short *pixel_ptr = (unsigned short *)dest->line[y];
      int x = 0;
      if( y & 1 ) {
          ++x;
          ++pixel_ptr;
      }
      for(; x <= fourth_width; ++x ) {
          //*pixel_ptr = color;
          pixel_ptr += 4;
      }
  }
17}

edited

wow
-------------------------------
i am who you are not am i

Evert

Member #794

November 2000

Nope - that masks out alternate scanlines (and can therefore be optimised considerably). That could also work to achieve the same effect though..

piccolo

Member #3,163

January 2003

yeah i fix the color from 255 0 255 to 0 0 0

wow
-------------------------------
i am who you are not am i

Arthur Kalliokoski

Second in Command

February 2005

A lot of the video cut scenes from mid-90's games such as Tomb Raider I used alternate scan lines to improve frame rate, it'd look much better with higher resolutions but still a bit dark. In other words, half the scan lines were black and built to stay that way.

They all watch too much MSNBC... they get ideas.

Kikaru

Member #7,616

August 2006

Quote:

That's providing of course the loop takes 5 milliseconds, which it won't on all machines. Which is why you don't use rest() for timing.

It's called an "example".

LennyLen

Member #5,313

December 2004

Quote:

It's called an "example".

I'm aware of that. But your example doesn't explain very well why not to use rest().

ImLeftFooted

Member #3,935

October 2003

Anything wrong with taking a screenshot of the game, tinting it, and displaying that?

As for code that will do this... ugh.. (/me goes to lookup random source code...)

Alright found it. Heres some code i found in old code and (lucky you) rewritten for your uses!

// If howMuch is 1, dest is turned black.  If howMuch is 0, dest is left unchanged
void shade(BITMAP *dest, float howMuch)
{
    const int val = (int)(howMuch * 0xff);

    set_trans_blender(0xff, 0xff, 0xff, val);
    drawing_mode(DRAW_MODE_TRANS, 0, 0, 0);
    rectfill(dest, 0, 0, dest->w, dest->h, makeacol32(0xff, 0xff, 0xff, val));
    drawing_mode(DRAW_MODE_SOLID, 0, 0, 0);
}

Shesh I spend more time writing code in this little a.cc textbox then I do anywhere else.

Example usage:

.. blah draw to screen ..

shade(screen, .5);

.. blah draw pause crap to screen ..

How is my posting?

gnolam

Member #2,030

March 2002

Quote:

Anything wrong with taking a screenshot of the game, tinting it, and displaying that?

It's much more work than just drawing a DRAW_MODE_TRANS rectfill() over the buffer?

[EDIT]

Quote:

rectfill(dest, 0, 0, dest->w, dest->h, makeacol32(0xff, 0xff, 0xff, val));

... and that alpha is completely unnecessary.

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Move to the Democratic People's Republic of Vivendi Universal (formerly known as Sweden) - officially democracy- and privacy-free since 2008-06-18!

ImLeftFooted

Member #3,935

October 2003

The docs don't really say so I just put the alpha value everywhere I could. Never actually tested which one is actually used.

How is my posting?