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apps/viewstl/README.md

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+# ViewSTL
+
+A simple viewer to render 3D models on-screen. The STL files have to be of the ASCII (non-binary) type. The rendering process can become quite slow
+for models with more than ~200-300 facets.
+
+The app contains a number of inlined C routines and makes use of the microcontroller's FPU. Therefore, the app installed on the watch contains a base64 encoded binary
+blob with those routines. The full C code is provided on github.
+
+## Controls
+
+The app supports 4 different rendering modes, swiping right-to-left on the touch screen cycles through them:
+- shaded polygons
+- shaded polygons with edge highlighting
+- wireframe, only edges between non-coplanar facets visible
+- wireframe, all facet (triangle) edges visible
+
+There are two different rotation modes that slightly alter the function of buttons 1 and 3, swiping left-to-right toggles between the two modes:
+- free rotation: button 1 zooms in, button 3 out
+- Z-axis (vertical axis) rotation: buttons 1 and 3 tilt the Z-axis
+
+There is currently no interface to upload STL files to the watch, the web IDE storage icon can be used instead.
+A future version might contain rotation based on accelerometer/magnetometer readings.
+