Apply masks, blend effects, and tints
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The Group and Part* elements also provide tintColor, renderMode and blendMode attributes which are powerful ways of adjusting the appearance of sections of your watch face.

Use clipping masks with a render mode

renderMode was introduced in version 1 of WFF to achieve a clipping mask.

The renderMode can be applied to Group and Part* elements in the scene hierarchy. To best understand how this works, consider how the scene graph is rendered:

<Group>
  <Group>
    <PartDraw />
    <PartText />
  </Group>
  <PartImage />
</Group>

The watch face renderer draws the elements in order while traversing the scene tree.

When renderMode is applied to a node, the effect only applies within the parent Group of that node. Other nodes elsewhere in the graph are unaffected.

When no renderMode is specified, the default is SOURCE, which means that the element is drawn directly to the screen. However, when one or more elements are present in the parent node with MASK (or ALL) specified, then a different approach is used:

An off-screen canvas is created
All child elements with SOURCE set (which is the default) are drawn
1. All child elements that are part of the mask (MASK, ALL) are applied to the canvas to clip the resulting image.

Note that this means that the order of the elements in the parent node are not taken into account.

In the following example, the Scene parent contains three children:

The first and third elements are MASK elements, so they're combined together to form a masking layer
The second element is the only non-masking layer

<WatchFace width="450" height="450">
  <Scene>
    <PartDraw x="175" y="50" width="100" height="100" renderMode="MASK">
      <Ellipse x="0" y="0" width="100" height="100">
        <Fill color="#FFFFFF"></Fill>
      </Ellipse>
    </PartDraw>

    <PartDraw x="0" y="0" width="450" height="450">
      <Rectangle x="0" y="0" width="450" height="450">
        <Fill color="#ff0000">
          <LinearGradient startX="0" startY="0" endX="450" endY="450"
            colors="..." positions="..." />
        </Fill>
      </Rectangle>
    </PartDraw>

    <PartText x="75" y="250" width="300" height="80" renderMode="MASK">
      <Text align="CENTER">
        <Font family="pacifico" size="72" weight="BOLD" color="#FFFFFF">Hello!</Font>
      </Text>
    </PartText>
  </Scene>
</WatchFace>

The third option for renderMode in addition to SOURCE and MASK is ALL. ALL specifies that the element should be treated both as a SOURCE and as a MASK which can be useful in some scenarios.

Use blend mode

Note: This capability is available on version 3 and higher of Watch Face Format.

From version 3, Watch Face Format offers the ability to apply a blend mode when composing Part* elements.

Unlike renderMode, which introduces a special mechanism for constructing the source and mask respectively, blendMode provides general access to all Android Graphics blend mode effects, and applies effects in the order that elements appear in the scene graph.

In normal operation, when a two Part* elements are placed in the scene, the top-most obscures or partially obscures the lower element because the default blendMode is SRC_OVER.

<PartDraw x="25" y="15" width="150" height="150">
  <Rectangle x="0" y="0" width="150" height="150">
    <Fill color="#ffd3ba" />
  </Rectangle>
</PartDraw>
<PartText x="35" y="60" width="300" height="120">
  <Text align="START">
    <Font family="pacifico" size="96" weight="BOLD" color="#fb5607">Hello!</Font>
  </Text>
</PartText>

As a demonstration of using blend modes, choosing SRC_ATOP, discards the source pixels that do not cover destination pixels. Namely, the PartText is the source, and the destination is the PartDraw.

So as a result, text is only drawn over the rectangle, and not elsewhere on the watch face:

<PartDraw x="25" y="15" width="150" height="150">
  <Rectangle x="0" y="0" width="150" height="150">
    <Fill color="#ffd3ba" />
  </Rectangle>
</PartDraw>
<PartText x="35" y="60" width="300" height="120" blendMode="SRC_ATOP">
  <Text align="START">
    <Font family="pacifico" size="96" weight="BOLD" color="#fb5607">Hello!</Font>
  </Text>
</PartText>

More complex effects can be applied, such as using COLOR_DODGE instead of SRC_ATOP, which makes destination brighter to reflect source.

An example of combining multiple Part* elements using HUE and COLOR_BURN blend modes:

<Group name="container" x="75" y="100" width="300" height="300">
  <PartDraw x="25" y="15" width="150" height="150">
    <Rectangle x="0" y="0" width="150" height="150">
      <Fill color="#ffd3ba" />
    </Rectangle>
  </PartDraw>
  <PartDraw x="100" y="15" width="150" height="150" blendMode="HUE">
    <Ellipse x="0" y="0" width="150" height="150">
      <Fill color="#219ebc" />
    </Ellipse>
  </PartDraw>
  <PartText x="35" y="60" width="300" height="120" blendMode="COLOR_BURN">
    <Text align="START">
      <Font family="pacifico" size="96" weight="BOLD" color="#fb5607">Hello!</Font>
    </Text>
  </PartText>
</Group>

Without any blendMode effects

With blendMode effects

Considerations

The following sections describe some considerations to keep in mind when using clipping and blend effects.

Blend mode is applied before render mode

If a node contains both Part elements using blendMode and Part elements using renderMode set to MASK (or ALL), then the following approach is taken.

The source is composited, including the application of blendMode modes
The mask is then applied from those elements specifying rendermode="MASK"

For example, considering the previous example used before, and adding in a rectangle mask, noting that the order of the masked element doesn't matter:

<Group name="container" x="75" y="100" width="300" height="300">
  <PartDraw x="25" y="15" width="150" height="150">
    <Rectangle x="0" y="0" width="150" height="150">
      <Fill color="#ffd3ba" />
    </Rectangle>
  </PartDraw>
  <PartDraw x="100" y="15" width="150" height="150" blendMode="HUE">
    <Ellipse x="0" y="0" width="150" height="150">
      <Fill color="#219ebc" />
    </Ellipse>
  </PartDraw>
  <PartDraw x="100" y="15" width="150" height="150" renderMode="MASK">
    <Rectangle x="0" y="0" width="150" height="150">
      <Fill color="#ffffff" />
    </Rectangle>
  </PartDraw>
  <PartText x="35" y="60" width="300" height="120" blendMode="COLOR_BURN">
    <Text align="START">
      <Font family="pacifico" size="96" weight="BOLD" color="#fb5607">Hello!</Font>
    </Text>
  </PartText>
</Group>

Performance

Using either renderMode and blendMode requires additional computation and drawing steps. Depending on the device on which the watch face is running, some of this may be executed efficiently in supported hardware, though this may not be possible on older devices.

For this reason, use renderMode and blendMode judiciously and be mindful of the impact that their use may have on the overall performance of the watch face.

Use tints

A tintColor can be applied to the whole Part* element, Group, or individual hands such as HourHand and MinuteHand, for example:

<WatchFace width="450" height="450">
  <Scene>
    <Group x="75" y="100" width="350" height="350" name="group1" tintColor="#ffd3ba">
      <PartDraw x="25" y="0" width="100" height="100">
        <Rectangle x="0" y="0" width="100" height="100">
          <Fill color="#ffffff" />
        </Rectangle>
      </PartDraw>
      <PartDraw x="150" y="0" width="100" height="100">
        <Ellipse x="25" y="0" width="100" height="100">
          <Fill color="#ffffff" />
        </Ellipse>
      </PartDraw>
      <PartText x="0" y="150" width="300" height="80">
        <Text align="CENTER">
          <Font family="pacifico" size="72" weight="BOLD" color="#ffffff">Hello!</Font>
        </Text>
      </PartText>
    </Group>
  </Scene>
</WatchFace>

This can be useful for styling an entire section of the watch face, including applying the style from the user settings, for example: tintcolor="[CONFIGURATION.myThemeColor.0]".

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