theme: create hover button fallbacks

...by copying the non-hover variant and adding a transparent overlay.

Co-authored-by: @johanmalm

include/common/graphic-helpers.h

@@ -47,4 +47,14 @@ void set_cairo_color(cairo_t *cairo, float *color);
 /* Draws a border with a specified line width */
 void draw_cairo_border(cairo_t *cairo, struct wlr_fbox fbox, double line_width);
 
+struct lab_data_buffer;
+
+struct surface_context {
+	bool is_duplicate;
+	cairo_surface_t *surface;
+};
+
+struct surface_context get_cairo_surface_from_lab_data_buffer(
+	struct lab_data_buffer *buffer);
+
 #endif /* LABWC_GRAPHIC_HELPERS_H */

include/common/string-helpers.h

@@ -2,6 +2,15 @@
 #ifndef LABWC_STRING_HELPERS_H
 #define LABWC_STRING_HELPERS_H
 
+/**
+ * trim_last_field() - Trim last field of string splitting on provided delim
+ * @buf: string to trim
+ * @delim: delimitator
+ *
+ * Example: With delim='_' and buf="foo_bar_baz" the return value is "foo_bar"
+ */
+void trim_last_field(char *buf, char delim);
+
 /**
  * string_strip - strip white space left and right
  * Note: this function does a left skip, so the returning pointer cannot be

src/buffer.c

@@ -129,6 +129,8 @@ buffer_create_wrap(void *pixel_data, uint32_t width, uint32_t height,
 {
 	struct lab_data_buffer *buffer = znew(*buffer);
 	wlr_buffer_init(&buffer->base, &data_buffer_impl, width, height);
+	buffer->unscaled_width = width;
+	buffer->unscaled_height = height;
 	buffer->data = pixel_data;
 	buffer->format = DRM_FORMAT_ARGB8888;
 	buffer->stride = stride;

src/common/graphic-helpers.c

@@ -3,8 +3,10 @@
 #include <assert.h>
 #include <cairo.h>
 #include <stdlib.h>
+#include <string.h>
 #include <wlr/types/wlr_scene.h>
 #include <wlr/util/box.h>
+#include "buffer.h"
 #include "common/graphic-helpers.h"
 #include "common/mem.h"
 
@@ -85,3 +87,32 @@ set_cairo_color(cairo_t *cairo, float *c)
 {
 	cairo_set_source_rgba(cairo, c[0], c[1], c[2], c[3]);
 }
+
+struct surface_context
+get_cairo_surface_from_lab_data_buffer(struct lab_data_buffer *buffer)
+{
+	/* Handle CAIRO_FORMAT_ARGB32 buffers */
+	if (buffer->cairo) {
+		return (struct surface_context){
+			.is_duplicate = false,
+			.surface = cairo_get_target(buffer->cairo),
+		};
+	}
+
+	/* Handle DRM_FORMAT_ARGB8888 buffers */
+	int w = buffer->unscaled_width;
+	int h = buffer->unscaled_height;
+	cairo_surface_t *surface =
+		cairo_image_surface_create(CAIRO_FORMAT_ARGB32, w, h);
+	if (!surface) {
+		return (struct surface_context){0};
+	}
+	unsigned char *data = cairo_image_surface_get_data(surface);
+	cairo_surface_flush(surface);
+	memcpy(data, buffer->data, h * buffer->stride);
+	cairo_surface_mark_dirty(surface);
+	return (struct surface_context){
+		.is_duplicate = true,
+		.surface = surface,
+	};
+}

src/common/string-helpers.c

@@ -6,6 +6,15 @@
 #include "common/mem.h"
 #include "common/string-helpers.h"
 
+void
+trim_last_field(char *buf, char delim)
+{
+	char *p = strrchr(buf, delim);
+	if (p) {
+		*p = '\0';
+	}
+}
+
 static void
 rtrim(char **s)
 {

src/theme.c

@@ -7,6 +7,7 @@
 
 #define _POSIX_C_SOURCE 200809L
 #include "config.h"
+#include <assert.h>
 #include <cairo.h>
 #include <ctype.h>
 #include <drm_fourcc.h>
@@ -56,6 +57,61 @@ drop(struct lab_data_buffer **buffer)
 	}
 }
 
+static void
+create_hover_fallback(struct theme *theme, struct lab_data_buffer **hover_buffer,
+		struct lab_data_buffer *icon_buffer)
+{
+	assert(icon_buffer);
+	assert(!*hover_buffer);
+
+	struct surface_context icon =
+		get_cairo_surface_from_lab_data_buffer(icon_buffer);
+	int icon_width = cairo_image_surface_get_width(icon.surface);
+	int icon_height = cairo_image_surface_get_height(icon.surface);
+
+	/* TODO: need to somehow respect rounded corners */
+	int width = SSD_BUTTON_WIDTH;
+	int height = theme->title_height;
+
+	if (width && height) {
+		/*
+		 * Proportionately increase size of hover_buffer if the
+		 * non-hover 'donor' buffer is larger than the allocated space.
+		 * It will get scaled down again by wlroots when rendered and as
+		 * required by the current output scale.
+		 *
+		 * This ensures that icons > width or > height keep their aspect
+		 * ratio and are rendered the same as without the hover overlay.
+		 */
+		double scale = MAX((double)icon_width / width,
+				(double)icon_height / height);
+		if (scale > 1.0f) {
+			width = (double)width * scale;
+			height = (double)height * scale;
+		}
+	}
+
+	*hover_buffer = buffer_create_cairo(width, height, 1.0, true);
+
+	cairo_t *cairo = (*hover_buffer)->cairo;
+	cairo_surface_t *surf = cairo_get_target(cairo);
+
+	/* Background */
+	cairo_set_source_surface(cairo, icon.surface,
+		(width - icon_width) / 2, (height - icon_height) / 2);
+	cairo_paint(cairo);
+
+	/* Overlay (non-multiplied alpha) */
+	set_cairo_color(cairo, (float[4]) { 0.5f, 0.5f, 0.5f, 0.3f});
+	cairo_rectangle(cairo, 0, 0, width, height);
+	cairo_fill(cairo);
+	cairo_surface_flush(surf);
+
+	if (icon.is_duplicate) {
+		cairo_surface_destroy(icon.surface);
+	}
+}
+
 /*
  * We use the following button filename schema: "BUTTON [TOGGLED] [STATE]"
  * with the words separted by underscore, and the following meaning:
@@ -204,6 +260,39 @@ load_buttons(struct theme *theme)
 				b->fallback_button, b->inactive.rgba);
 		}
 	}
+
+	/*
+	 * If hover-icons do not exist, add fallbacks by coping the non-hover
+	 * variant (base) and then adding an overlay.
+	 */
+	for (size_t i = 0; i < ARRAY_SIZE(buttons); i++) {
+		struct button *hover_button = &buttons[i];
+
+		if (!strstr(hover_button->name, "_hover")) {
+			continue;
+		}
+
+		/* If name=='foo_hover', basename='foo' */
+		char basename[64]  = {0};
+		snprintf(basename, sizeof(basename), "%s", hover_button->name);
+		trim_last_field(basename, '_');
+		for (size_t j = 0; j < ARRAY_SIZE(buttons); j++) {
+			struct button *base = &buttons[j];
+			if (!strcmp(basename, base->name)) {
+				if (!*hover_button->active.buffer) {
+					create_hover_fallback(theme,
+						hover_button->active.buffer,
+						*base->active.buffer);
+				}
+				if (!*hover_button->inactive.buffer) {
+					create_hover_fallback(theme,
+						hover_button->inactive.buffer,
+						*base->inactive.buffer);
+				}
+				break;
+			}
+		}
+	}
 }
 
 static int