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Principles

Pebble graphic library is based on layers hierarchy that manage drawn objects on screen. Each layer shall be redrawn when a dedicated callback is fired by Pebble mechanisms. Because of resources constraints, there is no actual partial redraw and the whole screen and every layers are all redrawn at once.

Then there is no actual layer bitmaps allowing to create z-layer as base for shadowing. A dedicated objects map is created to keep object information and position amongs layers. This map is then used to create shades and shadows.

Object representation

GColor8.rgb value are actually used as object identifiants that are placed on objects map, allowing pebble graphic primitive to be used. GShadow type is used as shadow objects, mapped directly to GColor8.

new_shadowing_object function provide a yet unused GShadow value and store in shadow_object_list the information on the object :

  • inner z (indice 0)

Objects map management

GBitmap *shadow_bitmap static bitmap is used as objects map. On first call to context switch (switch_to_shadow_ctx), it is allocated, along with the initialization of shadow_bitmap_ static variables, to match framebuffer bitmap size. Calls to context_switch (switch_to_shadow_ctx) and context revert (revert_to_fb_ctx) change context framebuffer bitmap to this objects map or back to initial framebuffer bitmap.

While on shadow bitmap context, standard pebble graphic function can be used to draw GShadow object on objects maps.

When the program is unloaded, shadow_bitmap must be de – allocated (call to destroy_shadow_ctx).

On the last call of the topmost layer rendering callback, the actual shadows can be created through the call to create_shadow. It computes for every framebuffer pixel :

  • on which object in the objects map is this pixel
    • whether this pixel is nearby a border of the object
      • on which side of the object the pixel is (bright side toward light, dark side is the shade)
      • apply color brightness modification accordingly
    • whether this pixel is of a object that create projective shadows
      • apply shading to pixel at shadow offset from the object.

Before starting a new screen rendering, or at the end of last screen rendering, objects map shall be cleared out (reset_shadow) to remove traces of previous objects.

Contributors & Contact

See README.

Copyright & Licence

See README.

Copyright (C): Baptiste Fouques 2016

Shadow Library is free software: you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

Shadow Library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU LesserGeneral Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with Shadow Library. If not, see http://www.gnu.org/licenses/.