Bitmap Draw Stacking

Bitmap Draw Stacking

Edgar Reynaldo

Major Reynaldo

May 2007

SiegeLord said:

Lastly, there is a function to simplify this process a bit:

ALLEGRO_TRANSFORM T;
al_build_transform(&T, this->getX() + this->width / 2, this->getY() + this->height / 2, this->getScale(), this->getScale(), this->getRotation());
al_use_transform(&T);
al_draw_bitmap(bmp, -this->width / 2, -this->height / 2, 0, 0);

It's missing the first translation, that's all. So it actually wouldn't work, because al_build_transform sets the identity first.

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Trent Gamblin

Member #261

April 2000

Elias said:

Why don't we have an al_draw_rotated_scaled_bitmap_region function? The function name is long, yes - and you can do the same thing with transformations. But we have all the other variants for doing it in a single function call so why not this?

I think it would be good, too. It's a fairly common thing to want to do, so it's a reasonable thing to add. If it weren't for the new test cases needed I could add it tomorrow. I haven't looked at adding test cases yet so I have no idea if it's a big deal. I might try it anyway if I remember this thread... but that's not a promise.

SiegeLord

Member #7,827

October 2006

Edgar Reynaldo said:

It's missing the first translation, that's all.

No, it's not. As my diagram showed, it got transfered to the coordinates passed to al_draw_bitmap:

ALLEGRO_TRANSFORM T;al_build_transform(&T, this->getX()+ this->width /2, this->getY()+ this->height /2, this->getScale(), this->getScale(), this->getRotation());al_use_transform(&T);al_draw_bitmap(bmp, -this->width / 2, -this->height / 2, 0, 0);

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Edgar Reynaldo

Major Reynaldo

May 2007

Wouldn't you have to modify the final translation in al_draw_bitmap to account for the scaling performed in al_build_transform though? And what about the rotation? It's scaled, then rotated about its top left corner, which is not what you want.

SiegeLord

Member #7,827

October 2006

Edgar Reynaldo said:

final translation in al_draw_bitmap

The translation in al_draw_bitmap is applied first, and then it is transformed using the current transformation. Doing it the other way wouldn't make any sense (it would make it clunky to use the transformations for a camera system, for example).

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Elias

Member #358

May 2000

Trent Gamblin said:

I think it would be good, too. It's a fairly common thing to want to do, so it's a reasonable thing to add. If it weren't forithe new test cases needed I could add it tomorrow. I haven't looked at adding test cases yet so I have no idea if it's a big deal. I might try it anyway if I remember this thread... but that'snot a promise.

I can also add it, just could have been that there's a reason against.
And yeah, we probably should make unit tests mandatory for any new additions

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