From 45e8503ead5aa90ee8f53ddf43257c019069653d Mon Sep 17 00:00:00 2001
From: Michael Jumper <mjumper@apache.org>
Date: Tue, 17 May 2016 20:49:51 -0700
Subject: [PATCH] GUACAMOLE-632: Dynamically scale JPEG/WebP quality depending
 on measured processing lag.

---
 src/common/surface.c | 48 +++++++++++++++++++++++++++++---------------
 1 file changed, 32 insertions(+), 16 deletions(-)

diff --git a/src/common/surface.c b/src/common/surface.c
index 8c690b75..c31dfbf0 100644
--- a/src/common/surface.c
+++ b/src/common/surface.c
@@ -78,13 +78,6 @@
 #define cairo_format_stride_for_width(format, width) (width*4)
 #endif
 
-/**
- * The JPEG image quality ('quantization') setting to use. Range 0-100 where
- * 100 is the highest quality/largest file size, and 0 is the lowest
- * quality/smallest file size.
- */
-#define GUAC_SURFACE_JPEG_IMAGE_QUALITY 90
-
 /**
  * The framerate which, if exceeded, indicates that JPEG is preferred.
  */
@@ -96,13 +89,6 @@
  */
 #define GUAC_SURFACE_JPEG_MIN_BITMAP_SIZE 4096
 
-/**
- * The WebP image quality ('quantization') setting to use. Range 0-100 where
- * 100 is the highest quality/largest file size, and 0 is the lowest
- * quality/smallest file size.
- */
-#define GUAC_SURFACE_WEBP_IMAGE_QUALITY 90
-
 /**
  * The JPEG compression min block size. This defines the optimal rectangle block
  * size factor for JPEG compression. Usually 8x8 would suffice, but use 16 to
@@ -1666,6 +1652,36 @@ static void __guac_common_surface_flush_to_png(guac_common_surface* surface,
 
 }
 
+/**
+ * Returns an appropriate quality between 0 and 100 for lossy encoding
+ * depending on the current processing lag calculated for the given client.
+ *
+ * @param client
+ *     The client for which the lossy quality is being calculated.
+ *
+ * @return
+ *     A value between 0 and 100 inclusive which seems appropriate for the
+ *     client based on lag measurements.
+ */
+static int guac_common_surface_suggest_quality(guac_client* client) {
+
+    int lag = guac_client_get_processing_lag(client);
+
+    /* Scale quality linearly from 90 to 30 as lag varies from 20ms to 80ms */
+    int quality = 90 - (lag - 20);
+
+    /* Do not exceed 90 for quality */
+    if (quality > 90)
+        return 90;
+
+    /* Do not go below 30 for quality */
+    if (quality < 30)
+        return 30;
+
+    return quality;
+
+}
+
 /**
  * Flushes the bitmap update currently described by the dirty rectangle within
  * the given surface directly via an "img" instruction as JPEG data. The
@@ -1702,7 +1718,7 @@ static void __guac_common_surface_flush_to_jpeg(guac_common_surface* surface) {
         /* Send JPEG for rect */
         guac_client_stream_jpeg(surface->client, socket, GUAC_COMP_OVER, layer,
                 surface->dirty_rect.x, surface->dirty_rect.y, rect,
-                GUAC_SURFACE_JPEG_IMAGE_QUALITY);
+                guac_common_surface_suggest_quality(surface->client));
 
         cairo_surface_destroy(rect);
         surface->realized = 1;
@@ -1764,7 +1780,7 @@ static void __guac_common_surface_flush_to_webp(guac_common_surface* surface,
         /* Send WebP for rect */
         guac_client_stream_webp(surface->client, socket, GUAC_COMP_OVER, layer,
                 surface->dirty_rect.x, surface->dirty_rect.y, rect,
-                GUAC_SURFACE_WEBP_IMAGE_QUALITY, 0);
+                guac_common_surface_suggest_quality(surface->client), 0);
 
         cairo_surface_destroy(rect);
         surface->realized = 1;