TouchInputMapper: Use a fixed scale factor for external drawing tablets
When using an external drawing tablet with a stylus, we expect there to
be a direct mapping between a subsection of the drawing tablet and the
entire display. In other words, we expect the user to be able to access
all parts of the display from within the drawing tablet surface.
We also expect to use the same scale factor in both directions so that angles
are preserved between the drawing tablet's space and the display space.
Moving a unit north on the drawing tablet should move the pointer by the
same amount on the display as moving a unit east.
External drawing tablets are almost always orientation un-aware. We
ensure that the active area of the drawing tablet is configured so that
the top-left point of that area (0, 0) always corresponds to the
top-left corner of the rotated display space.
Bug: 236798672
Test: atest inputflinger_tests
Test: Wacom Inutos S drawing tablet
Change-Id: I201874d66f276c57a7a7d0e23c14d5d13a2bf08d
diff --git a/services/inputflinger/reader/mapper/TouchInputMapper.cpp b/services/inputflinger/reader/mapper/TouchInputMapper.cpp
index 073c18b..50736aa 100644
--- a/services/inputflinger/reader/mapper/TouchInputMapper.cpp
+++ b/services/inputflinger/reader/mapper/TouchInputMapper.cpp
@@ -873,14 +873,26 @@
: ui::Transform();
// Step 4: Scale the raw coordinates to the display space.
- // - Here, we assume that the raw surface of the touch device maps perfectly to the surface
- // of the display panel. This is usually true for touchscreens.
+ // - In DIRECT mode, we assume that the raw surface of the touch device maps perfectly to
+ // the surface of the display panel. This is usually true for touchscreens.
+ // - In POINTER mode, we cannot assume that the display and the touch device have the same
+ // aspect ratio, since it is likely to be untrue for devices like external drawing tablets.
+ // In this case, we used a fixed scale so that 1) we use the same scale across both the x and
+ // y axes to ensure the mapping does not stretch gestures, and 2) the entire region of the
+ // display can be reached by the touch device.
// - From this point onward, we are no longer in the discrete space of the raw coordinates but
// are in the continuous space of the logical display.
ui::Transform scaleRawToDisplay;
const float xScale = static_cast<float>(mViewport.deviceWidth) / rotatedRawSize.width;
const float yScale = static_cast<float>(mViewport.deviceHeight) / rotatedRawSize.height;
- scaleRawToDisplay.set(xScale, 0, 0, yScale);
+ if (mDeviceMode == DeviceMode::DIRECT) {
+ scaleRawToDisplay.set(xScale, 0, 0, yScale);
+ } else if (mDeviceMode == DeviceMode::POINTER) {
+ const float fixedScale = std::max(xScale, yScale);
+ scaleRawToDisplay.set(fixedScale, 0, 0, fixedScale);
+ } else {
+ LOG_ALWAYS_FATAL("computeInputTransform can only be used for DIRECT and POINTER modes");
+ }
// Step 5: Undo the display rotation to bring us back to the un-rotated display coordinate space
// that InputReader uses.
diff --git a/services/inputflinger/reader/mapper/TouchInputMapper.h b/services/inputflinger/reader/mapper/TouchInputMapper.h
index bc358b9..cdd5124 100644
--- a/services/inputflinger/reader/mapper/TouchInputMapper.h
+++ b/services/inputflinger/reader/mapper/TouchInputMapper.h
@@ -821,6 +821,7 @@
static void assignPointerIds(const RawState& last, RawState& current);
+ // Compute input transforms for DIRECT and POINTER modes.
void computeInputTransforms();
void configureDeviceType();