Source
r/pebbledevelopers•
eric256

Rotating bitmaps

I'm trying to rotate a bitmap based on code from here but everytime I rotate the image at all I end up with a black box with some wierd graphics in it. If i set rotation to 0 it works fine:

s_white_bitmap = gbitmap_create_with_resource(RESOURCE_ID_IMAGE_ONE_WHITE);
s_black_bitmap = gbitmap_create_with_resource(RESOURCE_ID_IMAGE_ONE_BLACK);

GRect layer_frame = layer_get_frame(window_layer);

int angle = 0x1000 *  45 / 60;

s_white_layer = rot_bitmap_layer_create(s_white_bitmap);
s_black_layer = rot_bitmap_layer_create(s_black_bitmap);

layer_set_frame((Layer*)s_white_layer,layer_frame);  
layer_set_frame((Layer*)s_black_layer,layer_frame);  

rot_bitmap_set_compositing_mode(s_white_layer, GCompOpOr);  
rot_bitmap_set_compositing_mode(s_black_layer, GCompOpClear);

rot_bitmap_layer_set_angle(s_white_layer, angle);
rot_bitmap_layer_set_angle(s_black_layer, angle);


layer_add_child(window_layer, (Layer*)s_white_layer);
layer_add_child(window_layer, (Layer*)s_black_layer);

Any ideas why it would be black? Its a simple png with a transparent background.

Posted Aug 1, 2015, 6:27 AM UTC

35
ingrinder•
int angle = 0x1000 *  45 / 60

Should be

int angle = 0x10000 * 45 / 60

Or, alternatively, use the included macro definition:

int angle = TRIG_MAX_ANGLE * 45 / 60
1
eric256OP•

That does change the angle. However I still just end up with a black box instead of the image rotated.

1
ingrinder•

I think you're trying to draw a transparent png, but rot_bitmap_layer is deprecated and I don't think it supports setting the compositing mode. You should try using graphics_draw_rotated_bitmap or converting what look like your watchface's hands into GPaths and drawing them each time (which would use a somewhat considerable amount less of battery).

1
eric256OP•

Thanks for the tips. I'll try the GPaths method.

1
mereed•

another option, if you don't need to perform the rotation in real time, is simply rotate the image with a paint program and draw it on your pebble as you would any other image. for an example see my watchface "digital 90 flip" https://apps.getpebble.com/applications/5409756b950b217a0f000106

1