Increment a count variable in RenderScript

问题

I want to count the pixels of a bitmap using the following RenderScript code

RenderScript

Filename: counter.rs

#pragma version(1)
#pragma rs java_package_name(com.mypackage)
#pragma rs_fp_relaxed

uint count; // initialized in Java
void countPixels(uchar4* unused, uint x, uint y) {
  rsAtomicInc(&count);
}

Java

Application context = ...; // The application context
RenderScript rs = RenderScript.create(applicationContext);

Bitmap bitmap = ...; // A random bitmap
Allocation allocation = Allocation.createFromBitmap(rs, bitmap);

ScriptC_Counter script = new ScriptC_Counter(rs);
script.set_count(0);
script.forEach_countPixels(allocation);

allocation.syncAll(Allocation.USAGE_SCRIPT);
long count = script.get_count();

Error

This is the error message I get:

ERROR: Address not found for count

Questions

• Why doesn't my code work?
• How can I fix it?

Links

• RenderScript (on developer.android.com)
• rsAtomicInc(uint* addr);

回答1:

As a side note, it is usually not a good practice to use atomic operations in parallel computing unless you have to. RenderScript actually provide the reduction kernel for this kind of application. Maybe you can give it a try.

There several problems with the code:

1. The variable "count" should have been declared "volatile"
2. countPixels should have been "void RS_KERNEL countPixels(uchar4 in)"
3. script.get_count() will not get you the up-to-date value of "count", you have to get the value back with an Allocation.

If you have to use rsAtomicInc, a good example is actually the RenderScript CTS tests:

AtomicTest.rs

AtomicTest.java

回答2:

Here is my working solution.

RenderScript

Filename: counter.rs

#pragma version(1)
#pragma rs java_package_name(com.mypackage)
#pragma rs_fp_relaxed

int32_t count = 0;
rs_allocation rsAllocationCount;

void countPixels(uchar4* unused, uint x, uint y) {
  rsAtomicInc(&count);
  rsSetElementAt_int(rsAllocationCount, count, 0);
}

• rsAtomicInc()
• rsSetElementAt_int()

Java

Context context = ...;
RenderScript renderScript = RenderScript.create(context);

Bitmap bitmap = ...; // A random bitmap
Allocation allocationBitmap = Allocation.createFromBitmap(renderScript, bitmap);
Allocation allocationCount = Allocation.createTyped(renderScript, Type.createX(renderScript, Element.I32(renderScript), 1));

ScriptC_Counter script = new ScriptC_Counter(renderScript);
script.set_rsAllocationCount(allocationCount);
script.forEach_countPixels(allocationBitmap);

int[] count = new int[1];
allocationBitmap.syncAll(Allocation.USAGE_SCRIPT);
allocationCount.copyTo(count);

// The count can now be accessed via
count[0];

来源：https://stackoverflow.com/questions/41288051/increment-a-count-variable-in-renderscript