From c85adb33d222cb80105bc8f79dd3b0001d712561 Mon Sep 17 00:00:00 2001
From: Pascal Massimino <pascal.massimino@gmail.com>
Date: Fri, 25 Nov 2016 15:31:54 +0100
Subject: [PATCH] vwebp: make 'd' key toggle the debugging of fragments

it actually disables the disposal / blending method
and just displays the raw delta values.
Useful for debugging.
TODO: Outline the refreshed area with a drawn rectangle?

Change-Id: I6f8cddd0aad8b953cff78a693ae7e8c31def010c
---
 README           | 1 +
 examples/vwebp.c | 9 ++++++++-
 man/vwebp.1      | 5 ++++-
 3 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/README b/README
index ba4e8c5d..908e5591 100644
--- a/README
+++ b/README
@@ -384,6 +384,7 @@ Options are:
 Keyboard shortcuts:
   'c' ................ toggle use of color profile
   'i' ................ overlay file information
+  'd' ................ disable blending & disposal (debug)
   'q' / 'Q' / ESC .... quit
 
 Building:
diff --git a/examples/vwebp.c b/examples/vwebp.c
index 0fddf725..17887f77 100644
--- a/examples/vwebp.c
+++ b/examples/vwebp.c
@@ -54,6 +54,7 @@ static struct {
   int done;
   int decoding_error;
   int print_info;
+  int only_deltas;
   int use_color_profile;
 
   int canvas_width, canvas_height;
@@ -252,6 +253,9 @@ static void HandleKey(unsigned char key, int pos_x, int pos_y) {
     // more involved though (need to save the previous frame).
     if (!kParams.has_animation) ClearPreviousFrame();
     glutPostRedisplay();
+  } else if (key == 'd') {
+    kParams.only_deltas = 1 - kParams.only_deltas;
+    glutPostRedisplay();
   }
 }
 
@@ -314,7 +318,9 @@ static void HandleDisplay(void) {
   glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
   glPixelStorei(GL_UNPACK_ROW_LENGTH, pic->u.RGBA.stride / 4);
 
-  if (prev->dispose_method == WEBP_MUX_DISPOSE_BACKGROUND ||
+  if (kParams.only_deltas) {
+    DrawCheckerBoard();
+  } else if (prev->dispose_method == WEBP_MUX_DISPOSE_BACKGROUND ||
       curr->blend_method == WEBP_MUX_NO_BLEND) {
     // glScissor() takes window coordinates (0,0 at bottom left).
     int window_x, window_y;
@@ -414,6 +420,7 @@ static void Help(void) {
          "Keyboard shortcuts:\n"
          "  'c' ................ toggle use of color profile\n"
          "  'i' ................ overlay file information\n"
+         "  'd' ................ disable blending & disposal (debug)\n"
          "  'q' / 'Q' / ESC .... quit\n"
         );
 }
diff --git a/man/vwebp.1 b/man/vwebp.1
index a7d5181f..4ec346a3 100644
--- a/man/vwebp.1
+++ b/man/vwebp.1
@@ -1,5 +1,5 @@
 .\"                                      Hey, EMACS: -*- nroff -*-
-.TH VWEBP 1 "June 23, 2016"
+.TH VWEBP 1 "November 25, 2016"
 .SH NAME
 vwebp \- decompress a WebP file and display it in a window
 .SH SYNOPSIS
@@ -59,6 +59,9 @@ Toggle use of color profile.
 .B 'i'
 Overlay file information.
 .TP
+.B 'd'
+Disable blending and disposal process, for debugging purposes.
+.TP
 .B 'q' / 'Q' / ESC
 Quit.