Physics
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| Library: uTouch-Physics Language: C Dependencies: [[http://opende.sourceforge.net/wiki/index.php/Main_Page|ODE]] |
Library: uTouch-Physics<<BR>> Language: C API, implementation TBD (C or C++ depending on what is acceptable for upstream dependencies in GTK+)<<BR>> Dependencies: [[http://opende.sourceforge.net/wiki/index.php/Main_Page|ODE]] or [[http://code.google.com/p/chipmunk-physics/|Chipmunk]], [[http://launchpad.net/utouch-geis|Geis]] <<TableOfContents(3)>> |
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| Screen coordinates make more sense than real-world coordinates. If you have a 30" monitor next to a 24" monitor, both with equal resolutions, scrolling should move the content the same amount in screen coordinates. To facilitate this, units of pixels are used for distance. | Screen coordinates make more sense than real-world coordinates. If you have a 30" monitor next to a 24" monitor, both with equal resolutions, scrolling should move the content the same amount in screen coordinates. To facilitate this, units of pixels are used for distance in internal physics calculations. When real-world units are used, the library will convert them to pixels internally before performing computation. |
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| == Types == | == Models == === Scrollview === This model may be used to facilitate calculations involving a scrollable view. The content is a rectangle, and the viewport is a rectangle whose area is a subset of the content. The content and viewport can be thought of as boxes. The viewport may be dragged within the content. The viewport cannot be dragged outside of the content. While the user is interacting with the viewport by scrolling on an input device, the viewport follows the scroll motion. When the scrolling ceases, the viewport will continue moving with the velocity it has until friction or the content boundary force the viewport to a stop. TODO: How can we add "bouncing" when the viewport hits the edge of the content area? == API Types == |
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| Handle for uTouch-Physics context | Handle for uTouch-Physics context. === uphys_model === Enum specifying the model of the uphys context. Values: * UPHYS_SCROLLVIEW === uphys_units === Enum specifying a unit type. Values: * UPHYS_MILLIMETER * UPHYS_PIXEL === uphys_point === Holds a point in two axes. === uphys_size === Holds dimensions in two axes of an object. |
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| === gravity === | === error: int === Error code from last function call. Set to 0 on success. === error_string: const char * === Error string from last function call. Set to "no error" on success. === gravity: float === |
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| === mm_multiplier: float === Scalar multiplier applied to parameters given in UPHYS_MILLIMETER units. Defaults to value read from dconf settings repository if available, and then to ''TBD''. This is roughly equivalent to the sensitivity of a trackpad. === mu: float === Friction constant. Defaults to value read from dconf settings repository if available, and then to ''TBD''. === simulation_step_size: float === Simulation step size in ms. Defaults to ''TBD'' (maybe 30 Hz). See [[http://gafferongames.com/game-physics/fix-your-timestep/|here]] for more info. === (scrollview) viewport_origin: uphys_point === The origin point of the viewport of the scrollview. The origin is defined as the point within the rectangle with the minimum values for both axes. === (scrollview) viewport_size: uphys_size === The size of the viewport of the scrollview. === (scrollview) content_origin: uphys_point === The origin point of the content of the scrollview. The origin is defined as the point within the rectangle with the minimum values for both axes. === (scrollview) content_size: uphys_size === The size of the content of the scrollview. |
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| === uphys *uphys_new_scrollview() === Create a new uphys context. Returns a new context or NULL on error. |
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=== void uphys_inject(uphys *uphys, GeisEvent event) === Inject an input event. An error will occur if the time of the event is earlier than the time of a previous uphys_update() call. === void uphys_update(uphys *uphys, time_t *time) === Perform simulation of model up to the time given. === uphys *uphys_new(uphys_model model) === Create a new uphys context for a the model. Returns a new context or NULL on error. == API Use Case Example == Implementing smooth scrolling in a document viewer. Setup steps: 1. Create a uphys context using uphys_new(UPHYS_SCROLLVIEW) 2. Set properties on the context for the origin and size of the content and viewport 3. Create a Geis context to receive drag events 4. Add a callback for uphys on the display refresh signal - Use OpenGL sync signal if available<<BR>> - Otherwise use a static timer at a reasonable interval (maybe 30 Hz) In Geis drag callbacks: 1. Call uphys_inject(). - For touchpads and independent devices use UPHYS_MILLIMETER units<<BR>> - For touchscreens use UPHYS_PIXEL units In the uphys callback: 1. Call uphys_update() with the current time 2. Get the new viewport origin using uphys_get_property() 3. Redraw the scrollview |
Library: uTouch-Physics
Language: C API, implementation TBD (C or C++ depending on what is acceptable for upstream dependencies in GTK+)
Dependencies: ODE or Chipmunk, Geis
Units
Screen coordinates make more sense than real-world coordinates. If you have a 30" monitor next to a 24" monitor, both with equal resolutions, scrolling should move the content the same amount in screen coordinates. To facilitate this, units of pixels are used for distance in internal physics calculations. When real-world units are used, the library will convert them to pixels internally before performing computation.
A 24" 1080p monitor is a typical size and resolution for a desktop computer. This works out to 3614 px/m in the diagonal direction. We will assume square pixels. Thus, a reasonable conversion from meters to pixels is about 3.5 MP/m (where MP is a mega-pixel, or 1000 pixels).
Models
Scrollview
This model may be used to facilitate calculations involving a scrollable view. The content is a rectangle, and the viewport is a rectangle whose area is a subset of the content. The content and viewport can be thought of as boxes. The viewport may be dragged within the content. The viewport cannot be dragged outside of the content.
While the user is interacting with the viewport by scrolling on an input device, the viewport follows the scroll motion. When the scrolling ceases, the viewport will continue moving with the velocity it has until friction or the content boundary force the viewport to a stop.
TODO: How can we add "bouncing" when the viewport hits the edge of the content area?
API Types
uphys
Handle for uTouch-Physics context.
uphys_model
Enum specifying the model of the uphys context.
Values:
- UPHYS_SCROLLVIEW
uphys_units
Enum specifying a unit type.
Values:
- UPHYS_MILLIMETER
- UPHYS_PIXEL
uphys_point
Holds a point in two axes.
uphys_size
Holds dimensions in two axes of an object.
uphys Properties
error: int
Error code from last function call.
Set to 0 on success.
error_string: const char *
Error string from last function call.
Set to "no error" on success.
gravity: float
Defaults to 34.3 MP/s2. This is calculated by multiplying the standard earth gravity of 9.8 m/s2 by the standard conversion from meters to pixels of 3.5 MP/m.
mm_multiplier: float
Scalar multiplier applied to parameters given in UPHYS_MILLIMETER units. Defaults to value read from dconf settings repository if available, and then to TBD.
This is roughly equivalent to the sensitivity of a trackpad.
mu: float
Friction constant. Defaults to value read from dconf settings repository if available, and then to TBD.
simulation_step_size: float
Simulation step size in ms. Defaults to TBD (maybe 30 Hz).
See here for more info.
(scrollview) viewport_origin: uphys_point
The origin point of the viewport of the scrollview.
The origin is defined as the point within the rectangle with the minimum values for both axes.
(scrollview) viewport_size: uphys_size
The size of the viewport of the scrollview.
(scrollview) content_origin: uphys_point
The origin point of the content of the scrollview.
The origin is defined as the point within the rectangle with the minimum values for both axes.
(scrollview) content_size: uphys_size
The size of the content of the scrollview.
Functions
int uphys_set_property(uphys *uphys, const char *name, void *value)
Set a property value.
Returns 0 if successful, non-zero on error.
int uphys_get_property(const uphys *uphys, const char *name, void *value)
Get a property value.
Returns 0 if successful, non-zero on error.
void uphys_inject(uphys *uphys, GeisEvent event)
Inject an input event.
An error will occur if the time of the event is earlier than the time of a previous uphys_update() call.
void uphys_update(uphys *uphys, time_t *time)
Perform simulation of model up to the time given.
uphys *uphys_new(uphys_model model)
Create a new uphys context for a the model.
Returns a new context or NULL on error.
API Use Case Example
Implementing smooth scrolling in a document viewer.
Setup steps:
- Create a uphys context using uphys_new(UPHYS_SCROLLVIEW)
- Set properties on the context for the origin and size of the content and viewport
- Create a Geis context to receive drag events
- Add a callback for uphys on the display refresh signal
- Use OpenGL sync signal if available
- Otherwise use a static timer at a reasonable interval (maybe 30 Hz)
In Geis drag callbacks:
- Call uphys_inject().
- For touchpads and independent devices use UPHYS_MILLIMETER units
- For touchscreens use UPHYS_PIXEL units
In the uphys callback:
- Call uphys_update() with the current time
- Get the new viewport origin using uphys_get_property()
- Redraw the scrollview
Multitouch/Physics (last edited 2012-06-14 19:28:34 by c-67-170-185-42)