special-draw

special-draw is a very small pebble library that lets you draw rotated and/or semi-transparent primitives and text.

Installation

pebble package install special-draw

You must be using a new-style project; install the latest pebble tool and SDK and run pebble convert-project on your app if you aren't.

Usage

Usage is quite simple:

1. Begin the special-draw procedure.
2. Draw whatever primitives/text you'd like to.
3. Add modifiers to achieve the desired effect.
4. End the special-draw procedure.

It should be noted that special-draw is a relatively cpu-heavy operation and takes about 24kb of memory. For this reason, it's generally better to use alternatives such as GPath when possible.

Example

graphics_draw_rect(ctx, GRect(32, 54, 80, 60));

// Begin the session.
GSpecialSession * session = graphics_context_begin_special_draw(ctx);

graphics_draw_rect(ctx, GRect(42, 64, 80, 60));

// Add modifiers as desired.
graphics_context_special_session_add_modifier(session, graphics_special_draw_create_opacity_modifier(GOpacity2));
graphics_context_special_session_add_modifier(session, graphics_special_draw_create_rotation_modifier(TRIG_MAX_ANGLE / 100));

// End the session.
graphics_context_end_special_draw(session);

The above code requires no further cleanup since special-draw instances are automatically destroyed after use.

API

Base API

GSpecialSession * graphics_context_begin_special_draw(GContext * ctx)

Begins a special-draw session. You must keep the returned pointer to the GSpecialSession as it is used to end the session.

void graphics_context_end_special_draw(GSpecialSession * session)

Ends this GSpecialSession and destroys the associated data structure, including all modifiers. You must call this exactly once for every special-draw session opened.

void graphics_context_special_session_set_compositing_mode(GSpecialSession * session, GCompOp compositing_mode)

Change the compositing mode used by the default draw implementation. This may not be honored by custom draw modifiers. Defaults are GCompOpSet for color and GCompOpAnd for B/W screens.

This is usually not necessary for color screens. See Caveats below for more information on compositing modes for B/W screens.

Modifier API

void graphics_context_special_session_add_modifier( GSpecialSession * session, GSpecialSessionModifier * modifier)

Add a modifier to the internal list of modifiers.

Note that there can only be one draw-type modifier, and attempting to add more will replace (and destroy) the previous one. (currently, the only effect that requires a draw-type modifier is rotation.)

Included Modifiers

special-draw-rotation.h

GSpecialSessionModifier * graphics_special_draw_create_rotation_modifier( int32_t angle)

Creates a rotation modifier. This is a draw-type modifier.

• Mixing a dithered opacity setting such as GOpacity1_5 with a rotation that is not a multiple of 90 degrees will lead to weird interference.
• Arbitrary center points for rotation are currently not supported. (this is low-hanging fruit—feel free to submit a pull request!)

special-draw-opacity.h

GSpecialSessionModifier * graphics_special_draw_create_opacity_modifier( GOpacity opacity);

Not supported on Aplite.

Creates an opacity modifier. This is a normal-type modifier.

Choose an opacity from this enum:

    typedef enum {
        GOpacity0,
        GOpacity0_5,
        GOpacity1,
        GOpacity1_5,
        GOpacity2,
        GOpacity2_5,
        GOpacity3
    } GOpacity;

0: completely invisible (somewhat pointless) to 3: fully visible

Intermediate stages lead to (checkerboarded) dithered transparency. This may lead to disappearing or dashed diagonal lines.

Making your own modifier

Modifiers get full access to the GBitmap which primitives were rendered to, and draw-type modifiers also get access to the GContext (as they are supposed to draw the GBitmap to the GContext.)

Modifiers are a struct, defined in special-draw.h, with the following structure:

(GSpecialSessionModifier) {
    bool overrides_draw;
    union {
        GSpecialSessionModifierCallback modifier_run;
        GSpecialSessionModifierDrawCallback modifier_draw;
    } action;
    void * context;
    GSpecialSessionModifierDestroyCallback destroy;
}

A pointer to this structure should be passed to graphics_context_special_session_add_modifier.

If overrides_draw is true, modifier_draw must be set. Otherwise, modifier_run must be set.

This is a bare-bones modifier example:

#include "special-draw-opacity.h"

static void prv_run_modifier(GSpecialSessionModifier * modifier,
        GBitmap * session_bitmap) {
    // Insert bitmap manipulation code here.
}

static void prv_destroy_modifier(GSpecialSessionModifier * modifier) {
    free(modifier->context);
    free(modifier);
}

GSpecialSessionModifier * graphics_special_draw_create_pointless_modifier() {
    GSpecialSessionModifier * mod = malloc(sizeof(GSpecialSessionModifier));
    mod->overrides_draw = false;
    mod->action.modifier_run = prv_run_modifier;
    mod->destroy = prv_destroy_modifier;
    mod->context = malloc(sizeof(uint8_t));
    *((uint8_t *) mod->context) = 42;
    return mod;
}

Caveats

• Nesting GSpecialSessions is not supported and probably won't be due to the high memory requirements.
• Settings apply to the entire GSpecialSession, not just the part drawn after they are applied.
• Since the B/W framebuffer does not natively support transparency, it it not possible to draw a mixed black-and-white image on B/W screens using this library. The created framebuffer is completely filled with black on these platforms, and you may want to use graphics_fill_rect to fill it with white for certain GCompOps.

Thanks

...to @mhungerford for creating pebble_offscreen_rendering_text_demo, which shows the concept behind offscreen rendering on Pebble.

Licensing information

This project is under the following license:

MIT License

Copyright (c) 2016 Johannes Neubrand

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

NOTE: This README.md file is adapted from https://github.com/Katharine/pebble-events/blob/master/README.md, which is under the MIT license:

MIT License

Copyright (c) 2016 Katharine Berry

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.