Optimize thumbnail rendering

Massive responsivity gains have been achieved here.

Rescaling performance doesn't seem to be particularly affected.

fastiv.c

@@ -548,6 +548,15 @@ on_key_press(G_GNUC_UNUSED GtkWidget *widget, GdkEventKey *event,
 	G_GNUC_UNUSED gpointer data)
 {
 	switch (event->state & gtk_accelerator_get_default_mod_mask()) {
+	case GDK_MOD1_MASK | GDK_SHIFT_MASK:
+		if (event->keyval == GDK_KEY_D) {
+			GtkSettings *settings = gtk_settings_get_default();
+			const char *property = "gtk-application-prefer-dark-theme";
+			gboolean set = FALSE;
+			g_object_get(settings, property, &set, NULL);
+			g_object_set(settings, property, !set, NULL);
+		}
+		break;
 	case GDK_CONTROL_MASK:
 		switch (event->keyval) {
 		case GDK_KEY_o:
@@ -837,12 +846,16 @@ toolbar_connect(int index, GCallback callback)
 	g_signal_connect_swapped(g.toolbar[index], "clicked", callback, NULL);
 }
 
-// TODO(p): The toolbar should not be visible in fullscreen,
+// TODO(p): The text and icons should be faded, unless the mouse cursor is
-// or show up only when the cursor reaches the bottom of the screen.
+// on the toolbar. However, GtkEventBox is of no use, because either buttons
-// Presumably, GtkOverlay could be used for this. Proximity-based?
+// steal our {enter,leave}-notify-events, or we steal all their input.
-// Might want to make the toolbar normally translucent.
+// Not even connecting to these signals on children works, insensitive buttons
-// TODO(p): The text and icons should be faded, unless the mouse cursor
+// will not trigger anything.
-// is on the toolbar.
+// TODO(p): The toolbar should not be visible in fullscreen, or should show up
+// only when the cursor reaches the top of the screen. Translucency sounds
+// like a good mechanism here. Presumably, GtkOverlay could be used for this,
+// but it faces the same problem as above--the input model sucks.
+// TODO(p): Simply hide it in fullscreen and add a replacement context menu.
 static GtkWidget *
 make_view_toolbar(void)
 {
@@ -1002,7 +1015,7 @@ main(int argc, char *argv[])
 		G_CALLBACK(on_button_press_view), NULL);
 	gtk_container_add(GTK_CONTAINER(view_scroller), g.view);
 
-	// Maybe our custom widgets should derive colours from the theme instead.
+	// TODO(p): Base most colours on the theme, and make this configurable.
 	g_object_set(gtk_settings_get_default(),
 		"gtk-application-prefer-dark-theme", TRUE, NULL);
 

fiv-browser.c

@@ -254,8 +254,12 @@ draw_row(FivBrowser *self, cairo_t *cr, const Row *row)
 				border.top + extents.height + border.bottom);
 		}
 
-		gtk_render_background(
+		// Performance optimization--specifically targeting the checkerboard.
-			style, cr, border.left, border.top, extents.width, extents.height);
+		if (cairo_image_surface_get_format(item->entry->thumbnail) !=
+				CAIRO_FORMAT_RGB24) {
+			gtk_render_background(style, cr, border.left, border.top,
+				extents.width, extents.height);
+		}
 
 		gtk_render_frame(style, cr, 0, 0,
 			border.left + extents.width + border.right,
@@ -306,8 +310,9 @@ rescale_thumbnail(cairo_surface_t *thumbnail, double row_height)
 
 	int projected_width = round(scale_x * width);
 	int projected_height = round(scale_y * height);
+	cairo_format_t cairo_format = cairo_image_surface_get_format(thumbnail);
 	cairo_surface_t *scaled = cairo_image_surface_create(
-		CAIRO_FORMAT_ARGB32, projected_width, projected_height);
+		cairo_format, projected_width, projected_height);
 
 	// pixman can take gamma into account when scaling, unlike Cairo.
 	struct pixman_f_transform xform_floating;
@@ -315,7 +320,8 @@ rescale_thumbnail(cairo_surface_t *thumbnail, double row_height)
 
 	// PIXMAN_a8r8g8b8_sRGB can be used for gamma-correct results,
 	// but it's an incredibly slow transformation
-	pixman_format_code_t format = PIXMAN_a8r8g8b8;
+	pixman_format_code_t format =
+		cairo_format == CAIRO_FORMAT_RGB24 ? PIXMAN_x8r8g8b8 : PIXMAN_a8r8g8b8;
 
 	pixman_image_t *src = pixman_image_create_bits(format, width, height,
 		(uint32_t *) cairo_image_surface_get_data(thumbnail),

fiv-io.c

@@ -2366,9 +2366,15 @@ read_spng_thumbnail(
 	}
 
 	struct spng_ihdr ihdr = {};
+	struct spng_trns trns = {};
 	spng_get_ihdr(ctx, &ihdr);
+	bool may_be_translucent = !spng_get_trns(ctx, &trns) ||
+		ihdr.color_type == SPNG_COLOR_TYPE_GRAYSCALE_ALPHA ||
+		ihdr.color_type == SPNG_COLOR_TYPE_TRUECOLOR_ALPHA;
+
 	cairo_surface_t *surface = cairo_image_surface_create(
-		CAIRO_FORMAT_ARGB32, ihdr.width, ihdr.height);
+		may_be_translucent ? CAIRO_FORMAT_ARGB32 : CAIRO_FORMAT_RGB24,
+		ihdr.width, ihdr.height);
 
 	cairo_status_t surface_status = cairo_surface_status(surface);
 	if (surface_status != CAIRO_STATUS_SUCCESS) {
@@ -2396,10 +2402,7 @@ read_spng_thumbnail(
 	}
 
 	// pixman can be mildly abused to do this operation, but it won't be faster.
-	struct spng_trns trns = {};
+	if (may_be_translucent) {
-	if (ihdr.color_type == SPNG_COLOR_TYPE_GRAYSCALE_ALPHA ||
-		ihdr.color_type == SPNG_COLOR_TYPE_TRUECOLOR_ALPHA ||
-		!spng_get_trns(ctx, &trns)) {
 		for (size_t i = size / sizeof *data; i--; ) {
 			const uint8_t *unit = (const uint8_t *) &data[i];
 			uint32_t a = unit[3],