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If you can contribute a patch I would gladly look at it.

I looked at it, find no real difference.

Replacing -O3 by -Os would make the library go from 460ko to 320ko.

-fprefetch-loop-arrays could be removed as it produced a warning saying the option is ignored.

BTW, there are three Android.mk
SDL_image/Android.mk
SDL_image/externals/libpng/Android.mk
SDL_image/externals/jpeg/Android.mk

But the SDL_image/Android.mk includes directly the png/jpg source, 
so, the presence of the other Android.mk is confusing.
... 

To be confirmed, but it seems that compiling 
separatly SDL_image (shared) / jpeg (static) and libpng (static) make an even smaller library 320 ko -> 250 ko.
---
It is also possible to remove the WRITE support from PNG (pnglibconf.h & scripts) for 30 ko ...
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Then the libraries png/jpeg from Pelya are older and also smaller.

Hello,

Here's what I am doing to get the SDL_image compiled with libraries :

externals libraries are built independently with : 

ndk-build APP_BUILD_SCRIPT=jni/SDL_image_hg/external/libpng-1.6.2/Android.mk
ndk-build APP_BUILD_SCRIPT=jni/SDL_image_hg/external/jpeg-9/Android.mk 

For jpeg/Android.mk and libpng/Android.mk : 
 add -Os flags

For SDL_image/Android.mk:
remove : LOCAL_SRC_FILES of png and jpeg

LOCAL_LDLIBS := -Lobj/local/armeabi -ljpeg -lpng

The correct way should be to use LOCAL_STATIC_LIBRARIES but it does not work !

Also, I would like to trigger the build of jpeg/png automatically from the SDL_image Android.mk.

Any idea ? 

thanks

So, the trick is to save the local path, then to call the .mk files. 

  1 my_LOCAL_PATH := $(call my-dir)
  2 
  3 include $(my_LOCAL_PATH)/external/jpeg-9/Android.mk
  4 include $(my_LOCAL_PATH)/external/libpng-1.6.2/Android.mk
  5 
  6 LOCAL_PATH := $(my_LOCAL_PATH)
  7 include $(CLEAR_VARS)
  8 ...

Created attachment 1915 [details]
patch on Android.mk

Here's a patch to build the png/jpeg/webp lib independently with their own Android.mk file.

In addition to the previous patch, if you add -Os:

+++ external/jpeg-9/Android.mk	
-LOCAL_CFLAGS += -O3 -fstrict-aliasing -fprefetch-loop-arrays
+LOCAL_CFLAGS += -Os -fstrict-aliasing -fprefetch-loop-arrays

+++ external/libpng-1.6.2/Android.mk	
-common_CFLAGS := ## -fomit-frame-pointer
+common_CFLAGS := -Os ## -fomit-frame-pointer


You will get a libSDL2_image of 275 ko instead of 460 ko.

Curiously, you wouldn't get this by only adding -Os to the old Android.mk!

I admit this is not so much important now that android libs are heavy, but the Android.mk file is now smaller, and it's not required anymore to make symlink of png/jpeg/webp to the jni directory.

can be close with https://hg.libsdl.org/SDL_image/rev/0c24466d7d81