Pivot

Pivot

scriptX

Member #6,574

November 2005

How can I pivot a bitmap so that it follows the mouse, like this? I've got:

pivot_sprite(buffer, playerbuffer[PLAYER_ARM],
     (playerx+(playerbuffer[PLAYER_CURRENTFACING]->w/2)),
     (playery+(playerbuffer[PLAYER_CURRENTFACING]->h/2)),
     16,
     5,
     itofix( ???????? ));

??????? Should be...

Pedro Avelar Gontijo

Member #5,372

January 2005

I didn't quite get what you want. Is it just a line? If so, do

line (bitmap, sprite_center_x, sprite_center_y, mouse_x, mouse_y, color);

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scriptX

Member #6,574

November 2005

Sorry, no it's a bitmap.

Thomas Harte

Member #33

April 2000

Otherwise look into atan2 and remember to convert the output of that (radians) correctly to the input of pivot_sprite (Allegro units in fixed point).

[My site] [Tetrominoes]

Pedro Avelar Gontijo

Member #5,372

January 2005

Then explain better what are you rotating
[edit]
Beaten and not understanding a thing
[edit]
Now understanding but still beaten

----------
兩隻老虎，兩隻老虎，跑得快!

scriptX

Member #6,574

November 2005

thanks thomas.

pedro: bitmap

[edit]
Negatory...

pivot_sprite(buffer, playerbuffer[PLAYER_ARM],
     (playerx+(playerbuffer[PLAYER_CURRENTFACING]->w/2)),
     (playery+(playerbuffer[PLAYER_CURRENTFACING]->h/2)),
     16,
     5,
     itofix(atan2((double)mouse_y, (double)mouse_x)));

It moves about 1 pixel.

Jonatan Hedborg

Member #4,886

July 2004

No idea what you want, but doesent

pivot_sprite(buffer, playerbuffer[PLAYER_ARM],
     (playerx+(playerbuffer[PLAYER_CURRENTFACING]->w/2)),
     (playery+(playerbuffer[PLAYER_CURRENTFACING]->h/2)),
     16,
     5,
     itofix(atan2((double)mouse_y, (double)mouse_x)));

require that atan2 returns an integer, when it (if we're talking math.h here) actually returns radians (double)?

scriptX

Member #6,574

November 2005

...
itofix((int)(atan2((double)mouse_y, (double)mouse_x))));

Still doesn't work (moves 1 pixel)

gnolam

Member #2,030

March 2002

Gah.

Thomas said:

Otherwise look into atan2 and remember to convert the output of that (radians) correctly to the input of pivot_sprite (Allegro units in fixed point).

1) Use ftofix(). Casting atan2's output to int will just throw away information (hint: how many integers are there between -π and +π?).

2) Convert between radians (period: 2π ) and Allegro units (period: 256).

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miran

Member #2,407

June 2002

Quote:

itofix((int)(atan2((double)mouse_y, (double)mouse_x))));

Hmm, wouldn't you want to convert to a local coordinate system for the sprite you want to pivot? Like this:

ftofix(radians_to_allegro_degrees(atan2(sprite_y - mouse_y, mouse_x - sprite_x))));

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scriptX

Member #6,574

November 2005

Quote:

2) Convert between radians (period: 2π ) and Allegro units (period: 256).

wtf?

[edit]
Let me rephrase that... I did read that 2π = 360 degrees (correct?). So are you saying that 2π = 256 Allegro units?

Jonatan Hedborg

Member #4,886

July 2004

Yes. One allegro "full circle" is 256 units.
Also, what mirian said is probably a good idea.

scriptX

Member #6,574

November 2005

I'm having trouble with this.

...
ftofix((atan2(playery - mouse_y, mouse_x - playerx)) * (128/3.14) ));

I chose 128 because it's half of 256. 180 is half of 360.

Kitty Cat

Member #2,815

October 2002

What's the trouble? Other than the 180 is an integer which may cause the compiler to return an integer, which would be 0 (or it may not, dunno).

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scriptX

Member #6,574

November 2005

...
ftofix((atan2(playery - mouse_y, mouse_x - playerx)) * (128.0/3.14) ));

KittyCat: It's not "following" the mouse. In fact, it appears to face the opposite direction and I've tried:

...
//     /
ftofix(- ((atan2(playery - mouse_y, mouse_x - playerx)) * (128.0/3.14) )));

[edit]
http://img386.imageshack.us/img386/2571/a4hj.jpg[/img]