buffer: replace get_data_ptr with {begin,end}_data_ptr_access

This new API allows buffer implementations to know when a user is
actively accessing the buffer's underlying storage. This is
important for the upcoming client-backed wlr_buffer implementation.

include/types/wlr_buffer.h

@@ -16,13 +16,16 @@ enum wlr_buffer_cap {
 };
 
 /**
- * Access a pointer to the allocated data from the underlying implementation,
- * its format and its stride.
+ * Get a pointer to a region of memory referring to the buffer's underlying
+ * storage. The format and stride can be used to interpret the memory region
+ * contents.
  *
- * The returned pointer should be pointing to a valid memory location for read
- * and write operations.
+ * The returned pointer should be pointing to a valid memory region for read
+ * and write operations. The returned pointer is only valid up to the next
+ * buffer_end_data_ptr_access call.
  */
-bool buffer_get_data_ptr(struct wlr_buffer *buffer, void **data,
+bool buffer_begin_data_ptr_access(struct wlr_buffer *buffer, void **data,
 	uint32_t *format, size_t *stride);
+void buffer_end_data_ptr_access(struct wlr_buffer *buffer);
 
 #endif

include/wlr/types/wlr_buffer.h

@@ -26,10 +26,11 @@ struct wlr_buffer_impl {
 	void (*destroy)(struct wlr_buffer *buffer);
 	bool (*get_dmabuf)(struct wlr_buffer *buffer,
 		struct wlr_dmabuf_attributes *attribs);
-	bool (*get_data_ptr)(struct wlr_buffer *buffer, void **data,
-		uint32_t *format, size_t *stride);
 	bool (*get_shm)(struct wlr_buffer *buffer,
 		struct wlr_shm_attributes *attribs);
+	bool (*begin_data_ptr_access)(struct wlr_buffer *buffer, void **data,
+		uint32_t *format, size_t *stride);
+	void (*end_data_ptr_access)(struct wlr_buffer *buffer);
 };
 
 /**
@@ -47,6 +48,7 @@ struct wlr_buffer {
 
 	bool dropped;
 	size_t n_locks;
+	bool accessing_data_ptr;
 
 	struct {
 		struct wl_signal destroy;

render/allocator.c

@@ -81,7 +81,8 @@ struct wlr_buffer *wlr_allocator_create_buffer(struct wlr_allocator *alloc,
 		return NULL;
 	}
 	if (alloc->buffer_caps & WLR_BUFFER_CAP_DATA_PTR) {
-		assert(buffer->impl->get_data_ptr);
+		assert(buffer->impl->begin_data_ptr_access &&
+			buffer->impl->end_data_ptr_access);
 	}
 	if (alloc->buffer_caps & WLR_BUFFER_CAP_DMABUF) {
 		assert(buffer->impl->get_dmabuf);

render/drm_dumb_allocator.c

@@ -128,8 +128,8 @@ create_err:
 	return NULL;
 }
 
-static bool drm_dumb_buffer_get_data_ptr(struct wlr_buffer *wlr_buffer, void **data,
-		uint32_t *format, size_t *stride) {
+static bool drm_dumb_buffer_begin_data_ptr_access(struct wlr_buffer *wlr_buffer,
+		void **data, uint32_t *format, size_t *stride) {
 	struct wlr_drm_dumb_buffer *buf = drm_dumb_buffer_from_buffer(wlr_buffer);
 	*data = buf->data;
 	*stride = buf->stride;
@@ -137,6 +137,10 @@ static bool drm_dumb_buffer_get_data_ptr(struct wlr_buffer *wlr_buffer, void **d
 	return true;
 }
 
+static void drm_dumb_buffer_end_data_ptr_access(struct wlr_buffer *wlr_buffer) {
+	// This space is intentionally left blank
+}
+
 static bool buffer_get_dmabuf(struct wlr_buffer *wlr_buffer,
 		struct wlr_dmabuf_attributes *attribs) {
 	struct wlr_drm_dumb_buffer *buf = drm_dumb_buffer_from_buffer(wlr_buffer);
@@ -153,7 +157,8 @@ static void buffer_destroy(struct wlr_buffer *wlr_buffer) {
 static const struct wlr_buffer_impl buffer_impl = {
 	.destroy = buffer_destroy,
 	.get_dmabuf = buffer_get_dmabuf,
-	.get_data_ptr = drm_dumb_buffer_get_data_ptr,
+	.begin_data_ptr_access = drm_dumb_buffer_begin_data_ptr_access,
+	.end_data_ptr_access = drm_dumb_buffer_end_data_ptr_access,
 };
 
 static const struct wlr_allocator_interface allocator_impl;

render/pixman/renderer.c

@@ -86,10 +86,11 @@ static struct wlr_pixman_buffer *create_buffer(
 	void *data = NULL;
 	uint32_t drm_format;
 	size_t stride;
-	if (!buffer_get_data_ptr(wlr_buffer, &data, &drm_format, &stride)) {
+	if (!buffer_begin_data_ptr_access(wlr_buffer, &data, &drm_format, &stride)) {
 		wlr_log(WLR_ERROR, "Failed to get buffer data");
 		goto error_buffer;
 	}
+	buffer_end_data_ptr_access(wlr_buffer);
 
 	pixman_format_code_t format = get_pixman_format_from_drm(drm_format);
 	if (format == 0) {
@@ -125,6 +126,33 @@ static void pixman_begin(struct wlr_renderer *wlr_renderer, uint32_t width,
 	struct wlr_pixman_renderer *renderer = get_renderer(wlr_renderer);
 	renderer->width = width;
 	renderer->height = height;
+
+	struct wlr_pixman_buffer *buffer = renderer->current_buffer;
+	assert(buffer != NULL);
+
+	void *data = NULL;
+	uint32_t drm_format;
+	size_t stride;
+	buffer_begin_data_ptr_access(buffer->buffer, &data, &drm_format, &stride);
+
+	// If the data pointer has changed, re-create the Pixman image. This can
+	// happen if it's a client buffer and the wl_shm_pool has been resized.
+	if (data != pixman_image_get_data(buffer->image)) {
+		pixman_format_code_t format = get_pixman_format_from_drm(drm_format);
+		assert(format != 0);
+
+		pixman_image_unref(buffer->image);
+		buffer->image = pixman_image_create_bits_no_clear(format,
+			buffer->buffer->width, buffer->buffer->height, data, stride);
+	}
+}
+
+static void pixman_end(struct wlr_renderer *wlr_renderer) {
+	struct wlr_pixman_renderer *renderer = get_renderer(wlr_renderer);
+
+	assert(renderer->current_buffer != NULL);
+
+	buffer_end_data_ptr_access(renderer->current_buffer->buffer);
 }
 
 static void pixman_clear(struct wlr_renderer *wlr_renderer,
@@ -413,6 +441,7 @@ static uint32_t pixman_get_render_buffer_caps(void) {
 
 static const struct wlr_renderer_impl renderer_impl = {
 	.begin = pixman_begin,
+	.end = pixman_end,
 	.clear = pixman_clear,
 	.scissor = pixman_scissor,
 	.render_subtexture_with_matrix = pixman_render_subtexture_with_matrix,

render/shm_allocator.c

@@ -31,8 +31,8 @@ static bool buffer_get_shm(struct wlr_buffer *wlr_buffer,
 	return true;
 }
 
-static bool shm_buffer_get_data_ptr(struct wlr_buffer *wlr_buffer, void **data,
-		uint32_t *format, size_t *stride) {
+static bool shm_buffer_begin_data_ptr_access(struct wlr_buffer *wlr_buffer,
+		void **data, uint32_t *format, size_t *stride) {
 	struct wlr_shm_buffer *buffer = shm_buffer_from_buffer(wlr_buffer);
 	*data = buffer->data;
 	*format = buffer->shm.format;
@@ -40,10 +40,15 @@ static bool shm_buffer_get_data_ptr(struct wlr_buffer *wlr_buffer, void **data,
 	return true;
 }
 
+static void shm_buffer_end_data_ptr_access(struct wlr_buffer *wlr_buffer) {
+	// This space is intentionally left blank
+}
+
 static const struct wlr_buffer_impl buffer_impl = {
 	.destroy = buffer_destroy,
 	.get_shm = buffer_get_shm,
-	.get_data_ptr = shm_buffer_get_data_ptr,
+	.begin_data_ptr_access = shm_buffer_begin_data_ptr_access,
+	.end_data_ptr_access = shm_buffer_end_data_ptr_access,
 };
 
 static struct wlr_buffer *allocator_create_buffer(

types/wlr_buffer.c

@@ -12,6 +12,9 @@
 void wlr_buffer_init(struct wlr_buffer *buffer,
 		const struct wlr_buffer_impl *impl, int width, int height) {
 	assert(impl->destroy);
+	if (impl->begin_data_ptr_access || impl->end_data_ptr_access) {
+		assert(impl->begin_data_ptr_access && impl->end_data_ptr_access);
+	}
 	buffer->impl = impl;
 	buffer->width = width;
 	buffer->height = height;
@@ -24,6 +27,8 @@ static void buffer_consider_destroy(struct wlr_buffer *buffer) {
 		return;
 	}
 
+	assert(!buffer->accessing_data_ptr);
+
 	wlr_signal_emit_safe(&buffer->events.destroy, NULL);
 
 	buffer->impl->destroy(buffer);
@@ -67,12 +72,23 @@ bool wlr_buffer_get_dmabuf(struct wlr_buffer *buffer,
 	return buffer->impl->get_dmabuf(buffer, attribs);
 }
 
-bool buffer_get_data_ptr(struct wlr_buffer *buffer, void **data,
+bool buffer_begin_data_ptr_access(struct wlr_buffer *buffer, void **data,
 		uint32_t *format, size_t *stride) {
-	if (!buffer->impl->get_data_ptr) {
+	assert(!buffer->accessing_data_ptr);
+	if (!buffer->impl->begin_data_ptr_access) {
 		return false;
 	}
-	return buffer->impl->get_data_ptr(buffer, data, format, stride);
+	if (!buffer->impl->begin_data_ptr_access(buffer, data, format, stride)) {
+		return false;
+	}
+	buffer->accessing_data_ptr = true;
+	return true;
+}
+
+void buffer_end_data_ptr_access(struct wlr_buffer *buffer) {
+	assert(buffer->accessing_data_ptr);
+	buffer->impl->end_data_ptr_access(buffer);
+	buffer->accessing_data_ptr = false;
 }
 
 bool wlr_buffer_get_shm(struct wlr_buffer *buffer,