ssd: allow arbitrary cairo pattern as titlebar background

The titlebar background is now first rendered to a 1px wide buffer,
then stretched horizontally. This allows vertical gradients to be used.

include/theme.h

@@ -8,7 +8,7 @@
 #ifndef LABWC_THEME_H
 #define LABWC_THEME_H
 
-#include <stdio.h>
+#include <cairo.h>
 #include <wlr/render/wlr_renderer.h>
 #include "ssd.h"
 
@@ -89,6 +89,18 @@ struct theme {
 		struct lab_img *button_imgs
 			[LAB_SSD_BUTTON_LAST + 1][LAB_BS_ALL + 1];
 
+		/*
+		 * The titlebar background is specified as a cairo_pattern
+		 * and then also rendered into a 1px wide buffer, which is
+		 * stretched horizontally across the titlebar.
+		 *
+		 * This approach enables vertical gradients while saving
+		 * some memory vs. rendering the entire titlebar into an
+		 * image. It does not work for horizontal gradients.
+		 */
+		cairo_pattern_t *titlebar_pattern;
+		struct lab_data_buffer *titlebar_fill;
+
 		struct lab_data_buffer *corner_top_left_normal;
 		struct lab_data_buffer *corner_top_right_normal;
 

src/ssd/ssd-titlebar.c

@@ -35,8 +35,8 @@ ssd_titlebar_create(struct ssd *ssd)
 	int width = view->current.width;
 	int corner_width = ssd_get_corner_width();
 
-	float *color;
 	struct wlr_scene_tree *parent;
+	struct wlr_buffer *titlebar_fill;
 	struct wlr_buffer *corner_top_left;
 	struct wlr_buffer *corner_top_right;
 	int active;
@@ -49,7 +49,7 @@ ssd_titlebar_create(struct ssd *ssd)
 		parent = subtree->tree;
 		active = (subtree == &ssd->titlebar.active) ?
 			THEME_ACTIVE : THEME_INACTIVE;
-		color = theme->window[active].title_bg_color;
+		titlebar_fill = &theme->window[active].titlebar_fill->base;
 		corner_top_left = &theme->window[active].corner_top_left_normal->base;
 		corner_top_right = &theme->window[active].corner_top_right_normal->base;
 		wlr_scene_node_set_enabled(&parent->node, active);
@@ -57,9 +57,8 @@ ssd_titlebar_create(struct ssd *ssd)
 		wl_list_init(&subtree->parts);
 
 		/* Background */
-		add_scene_rect(&subtree->parts, LAB_SSD_PART_TITLEBAR, parent,
+		add_scene_buffer(&subtree->parts, LAB_SSD_PART_TITLEBAR, parent,
-			MAX(width - corner_width * 2, 0), theme->titlebar_height,
+			titlebar_fill, corner_width, 0);
-			corner_width, 0, color);
 		add_scene_buffer(&subtree->parts, LAB_SSD_PART_TITLEBAR_CORNER_LEFT, parent,
 			corner_top_left, -rc.theme->border_width, -rc.theme->border_width);
 		add_scene_buffer(&subtree->parts, LAB_SSD_PART_TITLEBAR_CORNER_RIGHT, parent,
@@ -151,7 +150,8 @@ set_squared_corners(struct ssd *ssd, bool enable)
 	FOR_EACH_STATE(ssd, subtree) {
 		part = ssd_get_part(&subtree->parts, LAB_SSD_PART_TITLEBAR);
 		wlr_scene_node_set_position(part->node, x, 0);
-		wlr_scene_rect_set_size(wlr_scene_rect_from_node(part->node),
+		wlr_scene_buffer_set_dest_size(
+			wlr_scene_buffer_from_node(part->node),
 			MAX(width - 2 * x, 0), theme->titlebar_height);
 
 		part = ssd_get_part(&subtree->parts, LAB_SSD_PART_TITLEBAR_CORNER_LEFT);
@@ -299,8 +299,8 @@ ssd_titlebar_update(struct ssd *ssd)
 	int bg_offset = maximized || squared ? 0 : corner_width;
 	FOR_EACH_STATE(ssd, subtree) {
 		part = ssd_get_part(&subtree->parts, LAB_SSD_PART_TITLEBAR);
-		wlr_scene_rect_set_size(
+		wlr_scene_buffer_set_dest_size(
-			wlr_scene_rect_from_node(part->node),
+			wlr_scene_buffer_from_node(part->node),
 			MAX(width - bg_offset * 2, 0), theme->titlebar_height);
 
 		x = theme->window_titlebar_padding_width;
@@ -458,7 +458,7 @@ ssd_update_title(struct ssd *ssd)
 	bool title_unchanged = state->text && !strcmp(title, state->text);
 
 	const float *text_color;
-	const float *bg_color;
+	const float bg_color[4] = {0, 0, 0, 0}; /* ignored */
 	struct font *font = NULL;
 	struct ssd_part *part;
 	struct ssd_sub_tree *subtree;
@@ -474,7 +474,6 @@ ssd_update_title(struct ssd *ssd)
 			THEME_ACTIVE : THEME_INACTIVE;
 		dstate = active ? &state->active : &state->inactive;
 		text_color = theme->window[active].label_text_color;
-		bg_color = theme->window[active].title_bg_color;
 		font = active ?  &rc.font_activewindow : &rc.font_inactivewindow;
 
 		if (title_bg_width <= 0) {
@@ -492,7 +491,9 @@ ssd_update_title(struct ssd *ssd)
 		if (!part) {
 			/* Initialize part and wlr_scene_buffer without attaching a buffer */
 			part = add_scene_part(&subtree->parts, LAB_SSD_PART_TITLE);
-			part->buffer = scaled_font_buffer_create(subtree->tree);
+			part->buffer = scaled_font_buffer_create_for_titlebar(
+				subtree->tree, theme->titlebar_height,
+				theme->window[active].titlebar_pattern);
 			if (part->buffer) {
 				part->node = &part->buffer->scene_buffer->node;
 			} else {

src/theme.c

@@ -53,7 +53,7 @@ struct rounded_corner_ctx {
 	struct wlr_box *box;
 	double radius;
 	double line_width;
-	float *fill_color;
+	cairo_pattern_t *fill_pattern;
 	float *border_color;
 	enum corner corner;
 };
@@ -1109,10 +1109,24 @@ rounded_rect(struct rounded_corner_ctx *ctx)
 	}
 	cairo_close_path(cairo);
 	cairo_set_operator(cairo, CAIRO_OPERATOR_SOURCE);
-	set_cairo_color(cairo, ctx->fill_color);
+	/*
+	 * We need to offset the fill pattern vertically by the border
+	 * width to line up with the rest of the titlebar. This is done
+	 * by applying a transformation matrix to the pattern temporarily.
+	 * It would be better to copy the pattern, but cairo does not
+	 * provide a simple way to this.
+	 */
+	cairo_matrix_t matrix;
+	cairo_matrix_init_translate(&matrix, 0, -ctx->line_width);
+	cairo_pattern_set_matrix(ctx->fill_pattern, &matrix);
+	cairo_set_source(cairo, ctx->fill_pattern);
 	cairo_fill_preserve(cairo);
 	cairo_stroke(cairo);
 
+	/* Reset the fill pattern transformation matrix afterward */
+	cairo_matrix_init_identity(&matrix);
+	cairo_pattern_set_matrix(ctx->fill_pattern, &matrix);
+
 	/*
 	 * Stroke horizontal and vertical borders, shown by Xs and Ys
 	 * respectively in the figure below:
@@ -1215,6 +1229,33 @@ out:
 	return buffer;
 }
 
+static struct lab_data_buffer *
+create_titlebar_fill(cairo_pattern_t *pattern, int height)
+{
+	/* create 1px wide buffer to be stretched horizontally */
+	struct lab_data_buffer *fill = buffer_create_cairo(1, height, 1);
+
+	cairo_t *cairo = cairo_create(fill->surface);
+	cairo_set_source(cairo, pattern);
+	cairo_paint(cairo);
+	cairo_surface_flush(fill->surface);
+	cairo_destroy(cairo);
+
+	return fill;
+}
+
+static void
+create_backgrounds(struct theme *theme)
+{
+	for (int active = THEME_INACTIVE; active <= THEME_ACTIVE; active++) {
+		theme->window[active].titlebar_pattern = color_to_pattern(
+			theme->window[active].title_bg_color);
+		theme->window[active].titlebar_fill = create_titlebar_fill(
+			theme->window[active].titlebar_pattern,
+			theme->titlebar_height);
+	}
+}
+
 static void
 create_corners(struct theme *theme)
 {
@@ -1232,7 +1273,7 @@ create_corners(struct theme *theme)
 			.box = &box,
 			.radius = rc.corner_radius,
 			.line_width = theme->border_width,
-			.fill_color = theme->window[active].title_bg_color,
+			.fill_pattern = theme->window[active].titlebar_pattern,
 			.border_color = theme->window[active].border_color,
 			.corner = LAB_CORNER_TOP_LEFT,
 		};
@@ -1567,6 +1608,7 @@ theme_init(struct theme *theme, struct server *server, const char *theme_name)
 	paths_destroy(&paths);
 
 	post_processing(theme);
+	create_backgrounds(theme);
 	create_corners(theme);
 	load_buttons(theme);
 	create_shadows(theme);
@@ -1593,6 +1635,8 @@ theme_finish(struct theme *theme)
 	}
 
 	for (int active = THEME_INACTIVE; active <= THEME_ACTIVE; active++) {
+		zfree_pattern(theme->window[active].titlebar_pattern);
+		zdrop(&theme->window[active].titlebar_fill);
 		zdrop(&theme->window[active].corner_top_left_normal);
 		zdrop(&theme->window[active].corner_top_right_normal);
 		zdrop(&theme->window[active].shadow_corner_top);