In addition to lots of bug fixes and build improvements, here are the major changes in this release:

General:

• The SDL_RW* macros have been turned into functions that are available only in 2.0.10 and onward
• Added SDL_SIMDGetAlignment(), SDL_SIMDAlloc(), and SDL_SIMDFree(), to allocate memory aligned for SIMD operations for the current CPU
• Added SDL_RenderDrawPointF(), SDL_RenderDrawPointsF(), SDL_RenderDrawLineF(), SDL_RenderDrawLinesF(), SDL_RenderDrawRectF(), SDL_RenderDrawRectsF(), SDL_RenderFillRectF(), SDL_RenderFillRectsF(), SDL_RenderCopyF(), SDL_RenderCopyExF(), to allow floating point precision in the SDL rendering API.
• Added SDL_GetTouchDeviceType() to get the type of a touch device, which can be a touch screen or a trackpad in relative or absolute coordinate mode.
• The SDL rendering API now uses batched rendering by default, for improved performance
• Added SDL_RenderFlush() to force batched render commands to execute, if you're going to mix SDL rendering with native rendering
• Added the hint SDL_HINT_RENDER_BATCHING to control whether batching should be used for the rendering API. This defaults to "1" if you don't specify what rendering driver to use when creating the renderer.
• Added the hint SDL_HINT_EVENT_LOGGING to enable logging of SDL events for debugging purposes
• Added the hint SDL_HINT_GAMECONTROLLERCONFIG_FILE to specify a file that will be loaded at joystick initialization with game controller bindings
• Added the hint SDL_HINT_MOUSE_TOUCH_EVENTS to control whether SDL will synthesize touch events from mouse events
• Improved handling of malformed WAVE and BMP files, fixing potential security exploits

Linux:

• Removed the Mir video driver in favor of Wayland

iOS / tvOS:

• Added support for Xbox and PS4 wireless controllers in iOS 13 and tvOS 13
• Added support for text input using Bluetooth keyboards

Android:

• Added low latency audio using OpenSL ES
• Removed SDL_HINT_ANDROID_SEPARATE_MOUSE_AND_TOUCH (replaced by SDL_HINT_MOUSE_TOUCH_EVENTS and SDL_HINT_TOUCH_MOUSE_EVENTS) SDL_HINT_ANDROID_SEPARATE_MOUSE_AND_TOUCH=1, should be replaced by setting both previous hints to 0. SDL_HINT_ANDROID_SEPARATE_MOUSE_AND_TOUCH=0, should be replaced by setting both previous hints to 1.
• Added the hint SDL_HINT_ANDROID_BLOCK_ON_PAUSE to set whether the event loop will block itself when the app is paused.