WIP: Try to scale pictures using OpenGL

WIP: Need to learn scaling.

WIP: Will it work with the native GDK window?

WIP: Find out what in the name of fuck is Quartz doing.

2 files changed, 138 insertions, 0 deletions

diff --git a/fiv-view.c b/fiv-view.c
index 0025d47..b39adab 100644
--- a/fiv-view.c
+++ b/fiv-view.c
@@ -584,6 +584,137 @@ fiv_view_realize(GtkWidget *widget)
 	reload_screen_cms_profile(FIV_VIEW(widget), window);
 }
 
+#include <epoxy/gl.h>
+
+// TODO(p): Try to use OpenGL/epoxy to scale a surface weirdly, for starters.
+static bool
+try_gl(FivView *self, cairo_t *cr)
+{
+	GError *error = NULL;
+	GdkWindow *window = gtk_widget_get_window(GTK_WIDGET(self));
+	GdkGLContext *ctx = gdk_window_create_gl_context(window, &error);
+	if (!ctx) {
+		g_debug("%s", error->message);
+		g_error_free(error);
+		return false;
+	}
+
+	// TODO(p): Need at least OpenGL 2.1 for sRGB textures.
+	//  - GDK uses 1.1/1.5/3.3 in its shaders.
+	//     - This means OpenGL 2.0, 3.2, 3.3...
+	//     - Shaders have been introduced in core OpenGL 2.0:
+	//       https://www.khronos.org/opengl/wiki/History_of_OpenGL
+	//  - Apple gives at most 4.1 and has deprecated OpenGL completely,
+	//    so that's the practical ceiling.
+	//  - Apple does not support OpenGL ES directly.
+	//  - libepoxy doesn't have EGL support on macOS, may have GLX support.
+	//  - There are epoxy_gl_version() and epoxy_has_gl_extension().
+	if (!gdk_gl_context_realize(ctx, &error)) {
+		g_warning("%s", error->message);
+		g_error_free(error);
+		return false;
+	}
+
+	// TODO(p): Use glGetError() != GL_NO_ERROR (0), at least at the end,
+	// and possibly use that clue as a hint to use fallback rendering.
+	// It should actually be a queue.
+	//
+	// Alternatively, ARB_debug_output/KHR_debug are a bit too new.
+
+	gdk_gl_context_make_current(ctx);
+	int width = 200;
+	int height = 200;
+
+	// NOTE: I get 16384, quite decent.
+	// https://feedback.wildfiregames.com/report/opengl/feature/GL_MAX_TEXTURE_SIZE
+	GLint max;
+	glGetIntegerv(GL_MAX_TEXTURE_SIZE, &max);
+
+	// TODO(p): Create a texture for the source, and for the destination,
+	// and rescale the picture with a bi-cubic algorithm in sRGB.
+	// TODO(p): Pre-scale the texture, create the context externally.
+	// TODO(p): Check GL_MAX_TEXTURE_SIZE, it may not make sense to prescale
+	// if the result is truly huge, though I can use Cairo as a fallback.
+	// I can also, naturally, scale ad-hoc.
+	// I may not be even able to load the source texture...
+	enum { SRC, DEST };
+	GLuint textures[2];
+	glGenTextures(2, textures);
+
+	// https://stackoverflow.com/questions/25157306 0..1
+	// GL_TEXTURE_RECTANGLE seems very useful, OpenGL 3.1
+	glBindTexture(GL_TEXTURE_2D, textures[SRC]);
+	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
+	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
+	// TODO(p): Figure out how to do bi-cubic in OpenGL.
+	//  - IMG_texture_filter_cubic is somehow related to OpenGL ES,
+	//    and I do not have it on my system.
+	//  - Some shaders: https://www.shadertoy.com/view/MllSzX
+	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
+	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
+
+	// TODO(p): What is a framebuffer?
+	//  - FBOs are in core since OpenGL 3.0.
+	//  - glCheckFramebufferStatus() is not required to call.
+	// TODO(p): How do we get sRGB?
+	//  - GL_SRGB8_ALPHA8
+	//     - But see: https://stackoverflow.com/a/43333704/76313
+	//     - Is texture sampling (there should be any filtering)
+	//       done before or after fragment (i.e., pixel) shaders?
+	//  - Is GL_FRAMEBUFFER_SRGB necessary?
+	//  - GL_RGB10_A2 and GL_RGB10 don't have sRGB versions,
+	//    need to do it ourselves.
+	//     - GL_UNSIGNED_INT_10_10_10_2 + GL_UNSIGNED_INT_2_10_10_10_REV
+	//     - GL_RGB10_A2UI vs GL_RGB10_A2?
+	//        - The former isn't translated to 0..1, do not want.
+	//     - pixman can also only do ARGB32 for sRGB.
+	//     - Cairo doesn't support have transparency with RGB30.
+	//     - GL_RGB{,A}{,16F,32F} look better
+	//  - https://developer.apple.com/library/archive/releasenotes/MacOSX/WhatsNewInOSX/Articles/MacOSX10_11_2.html
+	//    They want GL_RGB{,A}16 on macOS. But maybe others will work, too.
+
+	// https://www.khronos.org/opengl/wiki/Texture#Swizzle_mask
+	// since OpenGL 3.3.
+	//  - I guess this won't work with RGB30.
+#if 0
+	glGenFramebuffers(1, &priv->frame_buffer);
+
+	// GL_UNSIGNED_INT_8_8_8_8 stands for native-endian, so to speak.
+	// GL_UNSIGNED_BYTE is big-endian.
+	//
+	// https://mail.gnome.org/archives/commits-list/2016-April/msg06169.html
+	// and other thread messages show how GDK tackles ARGB -> RGBA on ES.
+	//
+	// I actually only care about alpha placement...
+	// I also don't care all that much about vertical flipping.
+	//
+	// TODO(p): Test whether GTK+ OpenGL is broken on big-endian.
+	if (gdk_gl_context_get_use_es(priv->context))
+		glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, width, height, 0, GL_RGBA,
+			GL_UNSIGNED_BYTE, NULL);
+	else
+		glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, width, height, 0, GL_BGRA,
+			GL_UNSIGNED_BYTE, NULL);
+
+	glBindFramebuffer(GL_FRAMEBUFFER, priv->frame_buffer);
+	glFramebufferTexture2D(
+		GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, textures[DEST], 0);
+#endif
+
+	// ...
+
+	// TODO(p): Find out what scales here, if it's Cairo or GL.
+	gdk_cairo_draw_from_gl(
+		cr, window, textures[DEST], GL_TEXTURE, 1, 0, 0, width, height);
+	gdk_gl_context_make_current(ctx);
+
+	glDeleteTextures(2, textures);
+
+	gdk_gl_context_clear_current();
+	g_object_unref(ctx);
+	return true;
+}
+
 static gboolean
 fiv_view_draw(GtkWidget *widget, cairo_t *cr)
 {
@@ -661,6 +792,12 @@ fiv_view_draw(GtkWidget *widget, cairo_t *cr)
 #endif  // GDK_WINDOWING_QUARTZ
 
 	cairo_paint(cr);
+
+	// XXX: GL would benefit from excluding the image area from
+	// gtk_render_background(), but then translucency wouldn't work.
+	// The naïve solution for that is rendering the background offscreen
+	// and recombining later (i.e., custom double-buffering).
+	try_gl(self, cr);
 	return TRUE;
 }
 
diff --git a/meson.build b/meson.build
index 2d854e7..6a1bb61 100644
--- a/meson.build
+++ b/meson.build
@@ -36,6 +36,7 @@ gdkpixbuf = dependency('gdk-pixbuf-2.0', required : get_option('gdk-pixbuf'))
 dependencies = [
 	dependency('gtk+-3.0'),
 	dependency('pixman-1'),
+	dependency('epoxy'),
 
 	dependency('libjpeg'),
 	dependency('libturbojpeg'),