From 9da428e0c03b32642233ceb8e282f731bf6ad44d Mon Sep 17 00:00:00 2001
From: Christopher Albert <albert@tugraz.at>
Date: Mon, 25 Aug 2025 11:15:02 +0200
Subject: [PATCH 1/3] update: reference issue #317 for colored_contours PDF
 crash

---
 BACKLOG.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/BACKLOG.md b/BACKLOG.md
index 147036db..33221e35 100644
--- a/BACKLOG.md
+++ b/BACKLOG.md
@@ -7,7 +7,7 @@
 **Infrastructure & Documentation Issues (Lower Priority)**
 
 ## DOING (Current Work)
-- [ ] Fix GitHub Pages deployment failure - colored_contours example crashes with "End of record" error at fortplot_pdf_drawing.f90:69 in pdf_write_color subroutine
+- [ ] #317: Fix GitHub Pages deployment failure - colored_contours PDF runtime crash in pdf_write_color
 
 ## BLOCKED (Infrastructure Issues)
 

From d84851fed34022d0b031cee98032c81c464d4ce1 Mon Sep 17 00:00:00 2001
From: Christopher Albert <albert@tugraz.at>
Date: Mon, 25 Aug 2025 11:18:33 +0200
Subject: [PATCH 2/3] fix: add robust RGB validation to pdf_write_color to
 prevent crashes

Add comprehensive validation to pdf_write_color subroutine to handle
invalid RGB values (NaN, infinity, out-of-range) gracefully. This
prevents 'End of record' crashes when color mapping produces invalid
values in contour plots.

- Use IEEE_ARITHMETIC intrinsic for NaN/infinity detection
- Clamp RGB values to valid [0.0, 1.0] range
- Default invalid values to black (0.0) for safety
- Fixes colored_contours example crash blocking GitHub Pages

Fixes #317
---
 src/fortplot_pdf_drawing.f90 | 31 +++++++++++++++++++++++++++++--
 1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/src/fortplot_pdf_drawing.f90 b/src/fortplot_pdf_drawing.f90
index 3a8830c9..0671a011 100644
--- a/src/fortplot_pdf_drawing.f90
+++ b/src/fortplot_pdf_drawing.f90
@@ -7,6 +7,7 @@ module fortplot_pdf_drawing
     !! Author: fortplot contributors
     
     use, intrinsic :: iso_fortran_env, only: wp => real64
+    use, intrinsic :: ieee_arithmetic, only: ieee_is_nan, ieee_is_finite
     use fortplot_vector, only: vector_stream_writer, vector_graphics_state
     use fortplot_markers, only: get_marker_size, MARKER_CIRCLE, MARKER_SQUARE, MARKER_DIAMOND, MARKER_CROSS
     implicit none
@@ -62,11 +63,37 @@ subroutine pdf_write_stroke(this)
     end subroutine pdf_write_stroke
 
     subroutine pdf_write_color(this, r, g, b)
-        !! Write PDF color command
+        !! Write PDF color command with robust validation
+        !! Validates and clamps RGB values to [0.0, 1.0] range
+        !! Handles NaN, infinity, and out-of-range values gracefully
         class(pdf_stream_writer), intent(inout) :: this
         real(wp), intent(in) :: r, g, b
+        real(wp) :: r_safe, g_safe, b_safe
         character(len=64) :: cmd
-        write(cmd, '(F0.3,1X,F0.3,1X,F0.3," RG")') r, g, b
+        
+        ! Validate and clamp R component
+        if (ieee_is_nan(r) .or. .not. ieee_is_finite(r)) then
+            r_safe = 0.0_wp  ! Default to black for invalid values
+        else
+            r_safe = max(0.0_wp, min(1.0_wp, r))  ! Clamp to [0, 1]
+        end if
+        
+        ! Validate and clamp G component
+        if (ieee_is_nan(g) .or. .not. ieee_is_finite(g)) then
+            g_safe = 0.0_wp  ! Default to black for invalid values
+        else
+            g_safe = max(0.0_wp, min(1.0_wp, g))  ! Clamp to [0, 1]
+        end if
+        
+        ! Validate and clamp B component
+        if (ieee_is_nan(b) .or. .not. ieee_is_finite(b)) then
+            b_safe = 0.0_wp  ! Default to black for invalid values
+        else
+            b_safe = max(0.0_wp, min(1.0_wp, b))  ! Clamp to [0, 1]
+        end if
+        
+        ! Write validated color values
+        write(cmd, '(F0.3,1X,F0.3,1X,F0.3," RG")') r_safe, g_safe, b_safe
         call this%add_to_stream(trim(cmd))
     end subroutine pdf_write_color
 

From 71e149643f45b9e609f9bcf4b21a3831fa77a967 Mon Sep 17 00:00:00 2001
From: Christopher Albert <albert@tugraz.at>
Date: Mon, 25 Aug 2025 11:24:44 +0200
Subject: [PATCH 3/3] plan: add code quality issues found in PR #318 review

---
 BACKLOG.md | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/BACKLOG.md b/BACKLOG.md
index 33221e35..4e65ff05 100644
--- a/BACKLOG.md
+++ b/BACKLOG.md
@@ -5,6 +5,9 @@
 **🚨 CRITICAL: User-visible PNG/PDF rendering completely broken**
 
 **Infrastructure & Documentation Issues (Lower Priority)**
+- [ ] #319: Refactor - investigate source of invalid RGB values in contour color mapping
+- [ ] #320: Feature - add debug logging for invalid color value corrections  
+- [ ] #321: Refactor - apply consistent validation pattern to other PDF write functions
 
 ## DOING (Current Work)
 - [ ] #317: Fix GitHub Pages deployment failure - colored_contours PDF runtime crash in pdf_write_color