[Feature Request] - Support for custom mouse cursors in sokol_app

[jeffkdev]

Sokol is close to supporting custom cursors icons with the addition of #78. I made a minimal implementation for Windows here
jeffkdev@54a44d9. I was thinking it would probably need to be changed to use pooled identifiers like the sokol_gfx resources. Currently sokol_app doesn't have any pooled resources, but if that was the eventual plan I could update the example do that as well.

I wasn't sure if this was worth tracking separately from the request of integrating cursors from sokol_imgui (#459). It looks like the author of that ticket is using cursor features from imgui internals, but ideally would be available in sokol_app directly. But feel free to close this if it feels like a duplicate.

[floooh]

Looks like a good start. Yes, the cursor images should use a pool. The WIP multiwindow-branch has a sokol-gfx style pool integrated (for window objects), I can simply rip that out:

sokol/sokol_app.h

Lines 2641 to 2720 in 57688eb

	/*=== POOL IMPLEMENTATION ====================================================*/
	_SOKOL_PRIVATE void _sapp_init_pool(_sapp_pool_t* pool, int num) {
	SOKOL_ASSERT(pool && (num >= 1));
	/* slot 0 is reserved for the 'invalid id', so bump the pool size by 1 */
	pool->size = num + 1;
	pool->queue_top = 0;
	/* generation counters indexable by pool slot index, slot 0 is reserved */
	pool->gen_ctrs = (uint32_t*) SOKOL_CALLOC((size_t)pool->size, sizeof(uint32_t));
	SOKOL_ASSERT(pool->gen_ctrs);
	/* it's not a bug to only reserve 'num' here */
	pool->free_queue = (int*) SOKOL_CALLOC((size_t)num, sizeof(int));
	SOKOL_ASSERT(pool->free_queue);
	/* never allocate the zero-th pool item since the invalid id is 0 */
	for (int i = pool->size-1; i >= 1; i--) {
	pool->free_queue[pool->queue_top++] = i;
	}
	}
	_SOKOL_PRIVATE void _sapp_discard_pool(_sapp_pool_t* pool) {
	SOKOL_ASSERT(pool);
	SOKOL_ASSERT(pool->free_queue);
	SOKOL_FREE(pool->free_queue);
	pool->free_queue = 0;
	SOKOL_ASSERT(pool->gen_ctrs);
	SOKOL_FREE(pool->gen_ctrs);
	pool->gen_ctrs = 0;
	pool->size = 0;
	pool->queue_top = 0;
	}
	_SOKOL_PRIVATE int _sapp_pool_alloc_index(_sapp_pool_t* pool) {
	SOKOL_ASSERT(pool);
	SOKOL_ASSERT(pool->free_queue);
	if (pool->queue_top > 0) {
	int slot_index = pool->free_queue[--pool->queue_top];
	SOKOL_ASSERT((slot_index > 0) && (slot_index < pool->size));
	return slot_index;
	}
	else {
	/* pool exhausted */
	return _SAPP_INVALID_SLOT_INDEX;
	}
	}
	_SOKOL_PRIVATE void _sapp_pool_free_index(_sapp_pool_t* pool, int slot_index) {
	SOKOL_ASSERT((slot_index > _SAPP_INVALID_SLOT_INDEX) && (slot_index < pool->size));
	SOKOL_ASSERT(pool);
	SOKOL_ASSERT(pool->free_queue);
	SOKOL_ASSERT(pool->queue_top < pool->size);
	#ifdef SOKOL_DEBUG
	/* debug check against double-free */
	for (int i = 0; i < pool->queue_top; i++) {
	SOKOL_ASSERT(pool->free_queue[i] != slot_index);
	}
	#endif
	pool->free_queue[pool->queue_top++] = slot_index;
	SOKOL_ASSERT(pool->queue_top <= (pool->size-1));
	}
	/* allocate the slot at slot_index:
	- bump the slot's generation counter
	- create a resource id from the generation counter and slot index
	- set the slot's id to this id
	- set the slot's state to ALLOC
	- return the resource id
	*/
	_SOKOL_PRIVATE uint32_t _sapp_slot_alloc(_sapp_pool_t* pool, _sapp_slot_t* slot, int slot_index) {
	SOKOL_ASSERT(pool && pool->gen_ctrs);
	SOKOL_ASSERT((slot_index > _SAPP_INVALID_SLOT_INDEX) && (slot_index < pool->size));
	SOKOL_ASSERT(slot->id == SAPP_INVALID_ID);
	uint32_t ctr = ++pool->gen_ctrs[slot_index];
	slot->id = (ctr<<_SAPP_SLOT_SHIFT)|(slot_index & _SAPP_SLOT_MASK);
	return slot->id;
	}
	_SOKOL_PRIVATE int _sapp_slot_index(uint32_t id) {
	int slot_index = (int) (id & _SAPP_SLOT_MASK);
	SOKOL_ASSERT(_SAPP_INVALID_SLOT_INDEX != slot_index);
	return slot_index;
	}

[floooh]

Just linking this for cross-reference:

#678

...it's not "custom cursor images" just yet, instead hardwired/builtin cursor types as needed by Dear ImGui, but its another step in the general direction of user-provided mouse cursors.

[jeffkdev]

If anyone stumbles on this in the future, this is how you can do it on the current sokol version on Windows: jeffkdev@5dbc11b

sapp handles the sapp_win32_update_cursor call now so the application doesn't have to do anything with the event anymore.

Edit: icon bool was flipped in initial commit. Updated in this: jeffkdev@094e04f