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Web Expression, DPI, and Touch Input

Hosanna's web target renders a design-space scene, then maps browser input back into design coordinates. App code should use design points for layout, hit testing, and scroll math. The web platform handles browser scale, DPI, and pointer normalization.

Web design-space coordinate mapping

The web scene may be scaled inside the browser viewport, but pointer, wheel, ScrollView, and CollectionView math stays in Hosanna design coordinates.

Expression​

Use ?expression= to choose the presentation mode:

  • tv: default TV-style scene. The scene is not auto-scaled for browser form factors.
  • web: browser presentation mode with the scene scaled to fit the viewport.
  • phone: handheld presentation mode.
  • tablet: tablet presentation mode.

Unknown or empty values default to tv.

http://localhost:5170/?expression=phone

Expressions also drive AppConfig variant selection. For example, expression=phone uses app.config.phone.json when that file exists, then falls back through platform-specific and base config. See Cross-Platform Runtime Model.

Device Presets​

Use device=<preset> to start from a known phone, tablet, foldable, or TV profile. Presets supply expression, design size, DPI, orientation defaults, and adapter defaults.

http://localhost:5170/?device=iphone-15
http://localhost:5170/?device=galaxy-tab-s9&orientation=landscape

Explicit parameters win over preset defaults:

http://localhost:5170/?device=iphone-15&displayWidth=390&displayHeight=844

Common presets include iphone-se, iphone-15, iphone-15-pro-max, ipad-10, ipad-pro-12-9, galaxy-s24, galaxy-s24-ultra, galaxy-z-fold-open, galaxy-tab-s9, pixel-8, pixel-tablet, rokuhd, rokufhd, apple-tv, apple-tv-4k, android-tv, android-tv-1080p, and android-tv-4k.

Design Surface​

Use designWidth and designHeight to change the logical design surface. width and height are supported only as legacy fallbacks when the design* values are omitted.

?expression=phone&designWidth=390&designHeight=844

Use orientation=portrait to swap the design dimensions when needed.

?expression=phone&designWidth=1920&designHeight=1080&orientation=portrait

Use x and y to place the fixed stage in the browser viewport. These are CSS viewport offsets, not design-space coordinates.

?expression=web&designWidth=1280&designHeight=720&x=12&y=8

DPI​

Use dpi to set the physical pixel width of the output surface.

?designWidth=1920&dpi=3840

The DPI scale is dpi / designWidth, so dpi=3840 on a 1920-point design yields a scale of 2. Renderer DOM sizes and text measurement account for this, while app layout remains in design points.

For existing TV-authored screens on a phone-sized output, keep the TV design surface and change the expression/output:

?expression=phone&orientation=portrait&designWidth=1920&designHeight=1080&dpi=1179&adapters=touch,keyboard

For mobile-authored screens, use phone-sized logical values:

?expression=phone&orientation=portrait&designWidth=393&designHeight=852&dpi=1179&adapters=touch,keyboard

Input Adapters​

Web registers input adapters through InputAdapterManager. Use ?adapters= to limit the active adapters:

?adapters=keyboard,mouse,touch
?adapters=roku,touch
?adapters=webkeyboard

Valid names:

  • keyboard: browser keyboard events forwarded into Roku-style remote input.
  • webkeyboard: genuine browser keyboard input events, bypassing Roku remote semantics.
  • debug: debug hover/highlight input.
  • mouse: pointer hover, click, and wheel input.
  • touch: touch pointer input.
  • roku: web Roku emulation profile; enables the Roku input manager plus keyboard shims.

When touch is enabled without mouse, touch can also accept mouse pointer events for easier local testing.

Touch Remote Overlay​

Add showRemoteOverlay=true to show the web touch remote overlay. Compact modes use showRemoteOverlay=tiny or showRemoteOverlay=mini.

?expression=phone&showRemoteOverlay=true

The overlay provides d-pad, OK, Back, and scale controls for mobile testing. In non-TV expressions, stage scaling is owned by the web scene rather than by resizing the document body.

Pointer Normalization​

Mouse and touch adapters convert browser client coordinates into Hosanna design coordinates before finding a view, focusing a CollectionView item, or updating a ScrollView. Wheel deltas are also converted into design-space deltas.

This means:

  • App code should not multiply pointer positions by browser DPI.
  • CollectionView row bounds and ScrollView offsets should be treated as design points.
  • CSS transforms applied by the web scene are already accounted for by the input adapters.