[X11][SDL 2.0.22 and above] Missing touch up event when SDL_HINT_MOUSE_AUTO_CAPTURE is on.

[kalana-sahabandu]

Reproduction steps:

1. Compile following example SDL2 application using SDL 2.0.22 or above

#include "SDL.h"
#include <stdio.h>

int main(int argc, char *argv[]) {
    SDL_Window *window = NULL;
    SDL_Renderer *renderer = NULL;
    
        SDL_version compiled;
    SDL_version linked;

    // Get the version the program was compiled against
    SDL_VERSION(&compiled);

    // Get the version the program is linked against
    SDL_GetVersion(&linked);

    // Print versions
    printf("We compiled against SDL version %d.%d.%d ...\n",
           compiled.major, compiled.minor, compiled.patch);
    printf("But we are linking against SDL version %d.%d.%d.\n",
           linked.major, linked.minor, linked.patch);

    // Initialize SDL
    if (SDL_Init(SDL_INIT_VIDEO) < 0) {
        fprintf(stderr, "SDL could not initialize! SDL_Error: %s\n", SDL_GetError());
        return 1;
    }

    SDL_SetHint(SDL_HINT_MOUSE_FOCUS_CLICKTHROUGH, "1");
    SDL_SetHint(SDL_HINT_TOUCH_MOUSE_EVENTS, "0");
    SDL_SetHint(SDL_HINT_MOUSE_TOUCH_EVENTS, "0");

    // Create window
    window = SDL_CreateWindow("SDL Example", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, 640, 480, SDL_WINDOW_SHOWN);
    if (window == NULL) {
        fprintf(stderr, "Window could not be created! SDL_Error: %s\n", SDL_GetError());
        SDL_Quit();
        return 1;
    }

    // Create renderer for the window
    renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED);
    if (renderer == NULL) {
        SDL_DestroyWindow(window);
        fprintf(stderr, "Renderer could not be created! SDL Error: %s\n", SDL_GetError());
        SDL_Quit();
        return 1;
    }

    SDL_bool quit = SDL_FALSE;
    while (!quit) {
        SDL_Event e;
        while (SDL_PollEvent(&e) != 0) {
            if (e.type == SDL_QUIT) {
                quit = SDL_TRUE;
            } else if (e.type == SDL_MOUSEBUTTONDOWN || e.type == SDL_MOUSEBUTTONUP) {
                // Log mouse button events
                const char *state = (e.type == SDL_MOUSEBUTTONDOWN) ? "down" : "up";
                printf("Mouse button %d %s at (%d, %d)\n", e.button.button, state, e.button.x, e.button.y);
            } else if (e.type == SDL_FINGERDOWN || e.type == SDL_FINGERUP) {
                // Log touch events
                const char *state = (e.type == SDL_FINGERDOWN) ? "down" : "up";
                printf("Finger %lld %s at (%f, %f)\n", e.tfinger.fingerId, state, e.tfinger.x, e.tfinger.y);
            }
        }

        // Clear screen
        SDL_SetRenderDrawColor(renderer, 0xFF, 0xFF, 0xFF, 0xFF);
        SDL_RenderClear(renderer);

        // Render updated graphics
        SDL_RenderPresent(renderer);
    }

    // Clean up
    SDL_DestroyRenderer(renderer);
    SDL_DestroyWindow(window);
    SDL_Quit();
    return 0;
}

2. Open the application using terminal (This way we can see the logs)
3. Touch the SDL2 window using one finger and don't lift the finger (You'll see a log message for finger down event)
4. While the finger is touching the SDL2 window press any key on the mouse (You'll see two log messages for mouse up and down events)
5. Now release the finger that is touching the SDL2 window (No finger up event received)

Expected behavior: Finger up event received for the corresponding finger (SDL versions below 2.0.22)
Actual behavior: No Finger up event received for the corresponding finger

After bisecting between 2.0.20 and 2.0.22. Bisection was pointing the following commit which introduced SDL_HINT_MOUSE_AUTO_CAPTURE hint.

commit 5ff4243
Author: Sam Lantinga slouken@libsdl.org
Date: Thu Mar 17 17:39:46 2022 -0700

Added a hint to capture the mouse when mouse buttons are pressed, defaulting on

Fixes https://github.com/libsdl-org/SDL/issues/5301  

include/SDL_hints.h | 13 +++++++++++
src/events/SDL_mouse.c | 58 ++++++++++++++++++++++++++++++++++++------------
src/events/SDL_mouse_c.h | 1 +
3 files changed, 58 insertions(+), 14 deletions(-)

Thank you so much and have a wonderful day,
Kalana