Rough Book

random musings of just another computer nerd

Category: Android

Implementing pinch-zoom and pan/drag in an Android view on the canvas

I was trying to get pinch-zoom and panning working on an Android view today. Basically I was trying to implement the same behavior you see when you use Google Maps (for example). You can zoom in and pan around until the edge of the image, but no further. Also, if the image is fully zoomed out, you can’t pan the image. Implementing the pinch-zoom functionality was pretty easy. I found an example on StackOverflow. I then wanted to implement panning (or dragging) as well. However, I wasn’t able to easily find examples and tutorials for this functionality. I started with this example that comes from the third edition of the Hello, Android! book but I didn’t get too far. So I started playing around a little bit with the events and started writing some code from scratch (using the example from Hello, Android!) so that I could have a better idea of what was happening.

As I mentioned before, getting zoom to work was pretty easy. Implementing panning/dragging was the hard part. The major issues I encountered and subsequently fixed were the following:

  1. Panning continues indefinitely in all directions.
  2. When you zoom and then pan, stop, and then start again, the view jerks to a new position instead of panning from the existing position.
  3. Excessive panning towards the left and top can be constrained, but panning towards the right and bottom is not so easily constrained.

Once I fixed all the problems, I figured that it would be nice to document it for future reference, and I also think it would be a useful resource for others who have the same problem. Now a little disclaimer before I go any further: I’m not an Android expert and I’m really not that great with graphics; I just started it learning to program for Android this semester for one of my Masters electives. So there might be a better way of doing all this, and if there is, please let me know! Also, if you want to skip all the explanations and just see the code, you can skip to the last page.

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Rooting the G2

As some of you may already be aware, it appears that the G2 has some sort of “magic restore” (it’s not a rootkit) function that causes all changes to /system to be reverted. This means that you cannot remove any bundled bloatware. Even more troubling, it looks like the phone will perform the restore while it is running (i.e, you don’t need a reset). I haven’t turned on my G2, so this is what I’ve heard from people at XDA Developers. You can get temporary root on the devices, but after a little while (some people say minutes, others say hours; experiences seem to vary) root is lost. So it is possible that something is performing the restore while the phone is running.

Helpful folks on XDA Developers have posted the datasheet to the eMMC and another kind soul (damnoregonian) was able to get the value of the CSD register (the register that seems to control the behavior of the MMC): d00f00320f5903fffffffdff924040c8.

WP_GRP_SIZE[36:32] and WP_GRP_ENABLE[31:31] seem to be the bits that control the write-protect (per the datasheet). Currently these seem to be set to the default values per the data sheet (11111b and 1b). Clearing the bits should (theoretically) turn off the write protection. The value to do that would be d00f00320f5903fffffffde0124040c8. The CSD node is R/O and so you cannot echo to it directly. The only way to do it would be to write a kernel module/driver that writes to the register. Apparently the kernel exports a function called mmc_send_csd, and so one should be able to write to this register.

I’m tempted to write a kernel module that does just that. But since working at Intel I haven’t written any kernel drivers. Also while I did write drivers at Intel, I pretty much made modifications to what others before me had written, and so I never wrote one from scratch. I’m going to see if I can start on something this weekend… wish I was still in college… I had a lot more time then!

If this works (and that’s a big if), there’s still the issue of restores being done while the phone is in operation. That could cause a lot of inconsistency. So this might be a partial solution.

Either way, I’m sure someone will come up with a way to root the phone. But if there’s nothing by next Friday, I’m going to return the phone.

UPDATE

Someone posted updated specs. It looks like those bits are read-only. Bummer. Also, this from T-Mobile’s website:

Bellevue, Wash. — Oct. 7, 2010

As pioneers in Android-powered mobile devices, T-Mobile and HTC strive to support innovation. The T-Mobile G2 is a powerful and highly customizable Android-powered smartphone, which customers can personalize and make their own, from the look of their home screen to adding their favorite applications and more.

The HTC software implementation on the G2 stores some components in read-only memory as a security measure to prevent key operating system software from becoming corrupted and rendering the device inoperable. There is a small subset of highly technical users who may want to modify and re-engineer their devices at the code level, known as “rooting,” but a side effect of HTC’s security measure is that these modifications are temporary and cannot be saved to permanent memory. As a result the original code is restored.

Well, T-Mobile. How about you provide us technical users a way to root our devices? What you’re doing is stupid. You’re going against everything Android stands for. If I can’t root it, I think I will return my phone and get a Vibrant instead. I would have expected this from Apple or Verizon. But not from you. Very disappointing.

Unboxing my new T-Mobile G2 Android Phone

My wife called me at work today and told me that my new phone just came in the mail :). It’s the new G2 by HTC, which is supposed to be the successor to the G1. The specs on this phone are:

  • 3.7 inch WVGA capacitive touch screen
  • 5 megapixel camera with auto-focus and flash
  • Qualcomm MSM7230 800MHz processor
  • 4GB ROM
  • 512MB RAM
  • GPS/aGPS
  • WiFi
  • Bluetooth
  • Android 2.2
  • Runs on T-Mobile’s 4G/HSPA+ network
  • Slide-out keyboard

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Download ShapeWriter APK

I tried to install ShapeWriter from the Android Marketplace yesterday and couldn’t find it (I was trying to reinstall it after flashing my phone with Cyanogenmod 5.0.8). After searching the interwebs, I found out that it had been removed from the marketplace on June 20th indefinitely (supposedly for QA issues). Luckily I had backed up the app using MyBackup Pro and still had the APK, so I was able to reinstall it. I’m putting the APK up here for anyone who needs to reinstall ShapeWriter.

Download ShapeWriter APK

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