Pre-scale loaded thumbnails, and only when needed

Stretch thumbnails by up to half a pixel so that they align nicely.

Make use of pixman's sRGB mode.

README.adoc

@@ -18,8 +18,8 @@ a package with the latest development version from Archlinux's AUR.
 Building and Running
 --------------------
 Build dependencies: Meson, pkg-config +
-Runtime dependencies: gtk+-3.0, shared-mime-info, libpng>=1.5.4, libturbojpeg,
+Runtime dependencies: gtk+-3.0, pixman-1, shared-mime-info, libpng>=1.5.4,
-LibRaw (optional)
+libturbojpeg, LibRaw (optional)
 
  $ git clone --recursive https://git.janouch.name/p/fastiv.git
  $ meson builddir

fastiv-browser.c

@@ -16,6 +16,7 @@
 //
 
 #include <math.h>
+#include <pixman.h>
 
 #include "fastiv-browser.h"
 #include "fastiv-io.h"
@@ -36,6 +37,8 @@ entry_free(Entry *self)
 		cairo_surface_destroy(self->thumbnail);
 }
 
+static const double g_row_height = 256;
+
 // --- Boilerplate -------------------------------------------------------------
 
 struct _FastivBrowser {
@@ -134,8 +137,6 @@ fastiv_browser_draw(GtkWidget *widget, cairo_t *cr)
 	gtk_render_background(gtk_widget_get_style_context(widget), cr, 0, 0,
 		allocation.width, allocation.height);
 
-	const double row_height = 256;
-
 	gint occupied_width = 0, y = 0;
 	for (guint i = 0; i < self->entries->len; i++) {
 		const Entry *entry = &g_array_index(self->entries, Entry, i);
@@ -144,28 +145,19 @@ fastiv_browser_draw(GtkWidget *widget, cairo_t *cr)
 
 		int width = cairo_image_surface_get_width(entry->thumbnail);
 		int height = cairo_image_surface_get_height(entry->thumbnail);
-
-		double scale = row_height / height;
-		if (width * scale > 2 * row_height)
-			scale = 2 * row_height / width;
-
-		int projected_width = round(scale * width);
-		int projected_height = round(scale * height);
-
 		if (occupied_width != 0 &&
-			occupied_width + projected_width > allocation.width) {
+			occupied_width + width > allocation.width) {
 			occupied_width = 0;
-			y += row_height;
+			y += g_row_height;
 		}
 
 		cairo_save(cr);
-		cairo_translate(cr, occupied_width, y + row_height - projected_height);
+		cairo_translate(cr, occupied_width, y + g_row_height - height);
-		cairo_scale(cr, scale, scale);
 		cairo_set_source_surface(cr, entry->thumbnail, 0, 0);
 		cairo_paint(cr);
 		cairo_restore(cr);
 
-		occupied_width += projected_width;
+		occupied_width += width;
 	}
 	return TRUE;
 }
@@ -203,6 +195,64 @@ fastiv_browser_init(FastivBrowser *self)
 	self->selected = -1;
 }
 
+static cairo_surface_t *
+rescale_thumbnail(cairo_surface_t *thumbnail)
+{
+	if (!thumbnail)
+		return thumbnail;
+
+	int width = cairo_image_surface_get_width(thumbnail);
+	int height = cairo_image_surface_get_height(thumbnail);
+
+	double scale_x = 1;
+	double scale_y = 1;
+	if (width > 2 * height) {
+		scale_x = 2 * g_row_height / width;
+		scale_y = round(scale_x * height) / height;
+	} else {
+		scale_y = g_row_height / height;
+		scale_x = round(scale_y * width) / width;
+	}
+	if (scale_x == 1 && scale_y == 1)
+		return thumbnail;
+
+	int projected_width = round(scale_x * width);
+	int projected_height = round(scale_y * height);
+	cairo_surface_t *scaled = cairo_image_surface_create(
+		CAIRO_FORMAT_ARGB32, projected_width, projected_height);
+
+	// pixman can take gamma into account when scaling, unlike Cairo.
+	struct pixman_f_transform xform_floating;
+	struct pixman_transform xform;
+
+	pixman_image_t *src = pixman_image_create_bits(
+		PIXMAN_a8r8g8b8_sRGB, width, height,
+		(uint32_t *) cairo_image_surface_get_data(thumbnail),
+		cairo_image_surface_get_stride(thumbnail));
+	pixman_image_t *dest = pixman_image_create_bits(
+		PIXMAN_a8r8g8b8_sRGB,
+		cairo_image_surface_get_width(scaled),
+		cairo_image_surface_get_height(scaled),
+		(uint32_t *) cairo_image_surface_get_data(scaled),
+		cairo_image_surface_get_stride(scaled));
+
+	pixman_f_transform_init_scale(&xform_floating, scale_x, scale_y);
+	pixman_f_transform_invert(&xform_floating, &xform_floating);
+	pixman_transform_from_pixman_f_transform(&xform, &xform_floating);
+	pixman_image_set_transform(src, &xform);
+	pixman_image_set_filter(src, PIXMAN_FILTER_BILINEAR, NULL, 0);
+	pixman_image_set_repeat(src, PIXMAN_REPEAT_PAD);
+
+	pixman_image_composite(PIXMAN_OP_SRC, src, NULL, dest, 0, 0, 0, 0, 0, 0,
+		projected_width, projected_height);
+	pixman_image_unref(src);
+	pixman_image_unref(dest);
+
+	cairo_surface_destroy(thumbnail);
+	cairo_surface_mark_dirty(scaled);
+	return scaled;
+}
+
 void
 fastiv_browser_load(FastivBrowser *self, const char *path)
 {
@@ -221,7 +271,8 @@ fastiv_browser_load(FastivBrowser *self, const char *path)
 		gchar *subpath = g_build_filename(path, filename, NULL);
 		g_array_append_val(self->entries,
 			((Entry){
-				.thumbnail = fastiv_io_lookup_thumbnail(subpath),
+				.thumbnail =
+					rescale_thumbnail(fastiv_io_lookup_thumbnail(subpath)),
 				.filename = subpath,
 			}));
 	}

meson.build

@@ -6,6 +6,7 @@ dependencies = [
 	dependency('gtk+-3.0'),
 	dependency('libturbojpeg'),
 	dependency('libpng', version : '>=1.5.4'),
+	dependency('pixman-1'),
 	libraw,
 	meson.get_compiler('c').find_library('m', required : false),
 ]