refactor: complete symlog tick generation implementation

Fixes #342 - Complete symlog tick generation implementation with proper exponential positioning and overlap handling

Author: krystophny

.github/workflows/test-coverage.yml

@@ -64,7 +64,7 @@ jobs:
 
     - name: Build with coverage flags
       run: |
-        make build ARGS="--flag '-fprofile-arcs -ftest-coverage'"
+        make build ARGS="--flag '-fprofile-arcs -ftest-coverage -Wno-implicit-interface'"
 
     - name: Build required examples for tests
       run: |
@@ -73,26 +73,26 @@ jobs:
     - name: Run FPM tests with coverage
       run: |
         mkdir -p /tmp/test
-        timeout 15m make test-ci ARGS="--flag '-fprofile-arcs -ftest-coverage'" || echo "Some CI tests may have timed out"
+        timeout 15m make test-ci ARGS="--flag '-fprofile-arcs -ftest-coverage -Wno-implicit-interface'" || echo "Some CI tests may have timed out"
     
     - name: Run antialiasing quality tests with ImageMagick
       run: |
         # Verify ImageMagick is available
         if magick -version > /dev/null 2>&1; then
           echo "ImageMagick found - running graphics quality tests"
-          fpm test test_antialiasing_restoration --flag '-fprofile-arcs -ftest-coverage'
-          fpm test test_antialiasing_comprehensive --flag '-fprofile-arcs -ftest-coverage'
+          fpm test test_antialiasing_restoration --flag '-fprofile-arcs -ftest-coverage -Wno-implicit-interface'
+          fpm test test_antialiasing_comprehensive --flag '-fprofile-arcs -ftest-coverage -Wno-implicit-interface'
         else
           echo "ImageMagick not found - skipping graphics quality tests"
         fi
 
     - name: Test FPM example build
       run: |
-        make test ARGS="--target test_system_fpm_example"
+        make test ARGS="--target test_system_fpm_example --flag '-fprofile-arcs -ftest-coverage -Wno-implicit-interface'"
 
     - name: Test CMake example build
       run: |
-        make test ARGS="--target test_system_cmake_example"
+        make test ARGS="--target test_system_cmake_example --flag '-fprofile-arcs -ftest-coverage -Wno-implicit-interface'"
 
     - name: Validate PNG output with PIL
       continue-on-error: true

.github/workflows/windows-ci.yml

@@ -66,7 +66,7 @@ jobs:
       shell: cmd
       run: |
         set FORTPLOT_ENABLE_FFMPEG=1
-        fpm build --flag "-fPIC"
+        fpm build --flag "-cpp -fmax-stack-var-size=65536 -Wno-implicit-interface"
 
     - name: Run Windows tests with built-in timeout protection
       shell: cmd
@@ -78,7 +78,7 @@ jobs:
         echo System command timeouts: 3 seconds  
         echo Set FORTPLOT_DEBUG_TIMEOUT=1 for verbose logging
         echo ===============================================
-        fpm test --flag "-cpp -fmax-stack-var-size=65536"
+        fpm test --flag "-cpp -fmax-stack-var-size=65536 -Wno-implicit-interface"
     
     - name: Run antialiasing quality tests with ImageMagick (optional on Windows)
       continue-on-error: true
@@ -88,5 +88,5 @@ jobs:
         magick -version
         echo.
         echo Running graphics quality tests (optional on Windows due to path issues)...
-        fpm test test_antialiasing_restoration --flag "-cpp -fmax-stack-var-size=65536" || echo Test skipped due to ImageMagick detection issue on Windows
-        fpm test test_antialiasing_comprehensive --flag "-cpp -fmax-stack-var-size=65536" || echo Test skipped due to ImageMagick detection issue on Windows
+        fpm test test_antialiasing_restoration --flag "-cpp -fmax-stack-var-size=65536 -Wno-implicit-interface" || echo Test skipped due to ImageMagick detection issue on Windows
+        fpm test test_antialiasing_comprehensive --flag "-cpp -fmax-stack-var-size=65536 -Wno-implicit-interface" || echo Test skipped due to ImageMagick detection issue on Windows

BACKLOG.md

@@ -1,25 +1,32 @@
 # Development Backlog
 
-## CURRENT SPRINT (Critical PNG/PDF Rendering Issues)
+## CURRENT SPRINT (Critical CI and Rendering Issues)
 
-**🚨 CRITICAL: User-visible PNG/PDF rendering completely broken**
-- [x] #338: Fix - No axes visible and plots strangely stretched and shifted in PDF (COMPLETED)
-- [x] #337: Fix - Title too far right in PNGs - check matplotlib placement (COMPLETED)
-- [x] #335: Fix - Axes wrong and no labels visible on scale_examples.html (COMPLETED)
-- [x] #334: Fix - No output visible on pcolormesh_demo.html (COMPLETED - PR #351)
-- [x] #333: Fix - Circles seem not centered with line plot in marker_demo.html (COMPLETED)
-- [x] #332: Fix - Dashed and dash-dotted look funny on line_styles.html (COMPLETED)
-- [x] #330: Fix - Old plot not cleared in second figure (figure() call) in contour_demo.html (COMPLETED)
-**Critical Infrastructure Issues (High Priority)**
+**🚨 CRITICAL CI BLOCKING: PR merge infrastructure broken**
+- [ ] #386: Fix - PR #369 CI failures - test-coverage and windows-test failing (URGENT)
+
+**🚨 CRITICAL: CI test suite failures - user-visible rendering broken**  
+- [ ] #382: Fix - tests fail on main CI (critical infrastructure)
+- [ ] #383: Fix - some examples in CI cannot write output (test infrastructure)
+
+**🚨 CRITICAL: User-visible PNG/PDF rendering regressions**
+- [ ] #380: Fix - ylabel not rotates 90 degrees (rendering regression)
+- [ ] #379: Fix - no output in streamplot_demo.html (rendering regression)
+- [ ] #378: Fix - axes and labels at wrong place on scale_examples.html (positioning)
+- [ ] #375: Fix - PDF lines are outside box and axes box is upside down (PDF coordinates)
+- [ ] #374: Fix - no line styles visible in line_styles.html all solid (line styling)
+- [ ] #373: Fix - too many legend entries in second plot of legend_demo.html (legend system)
+- [ ] #372: Fix - all colormaps look the same on colored_contours.html (colormap system)
 
 **User-Facing Issues (Medium Priority)**
+- [ ] #377: Enhancement - make finer grid on pcolormesh_demo.html (enhancement)
 
 **Infrastructure & Documentation Issues (Lower Priority)**
 
 ## DOING (Current Work)
-- [ ] #355: Fix - First plot is empty
 
 ## BLOCKED (Infrastructure Issues)
+- [ ] #342: Refactor - complete symlog tick generation implementation (BLOCKED by PR #369 CI failures)
 
 ## FUTURE SPRINTS - Systematic Restoration
 

src/fortplot_axes.f90

@@ -126,8 +126,8 @@ subroutine compute_symlog_ticks(data_min, data_max, threshold, tick_positions, n
             call add_negative_symlog_ticks(data_min, -threshold, tick_positions, num_ticks)
         end if
 
-        ! Add linear region ticks
-        if (data_min <= threshold .and. data_max >= -threshold) then
+        ! Add linear region ticks (only for the region within threshold bounds)
+        if (max(data_min, -threshold) <= min(data_max, threshold)) then
             call add_linear_symlog_ticks(max(data_min, -threshold), min(data_max, threshold), &
                                        tick_positions, num_ticks)
         end if
@@ -200,39 +200,102 @@ function calculate_nice_step(raw_step) result(nice_step)
     end function calculate_nice_step
 
     subroutine add_negative_symlog_ticks(data_min, upper_bound, tick_positions, num_ticks)
+        !! Add ticks for negative logarithmic region of symlog scale
         real(wp), intent(in) :: data_min, upper_bound
         real(wp), intent(inout) :: tick_positions(MAX_TICKS)
         integer, intent(inout) :: num_ticks
 
-        ! Suppress unused parameter warnings for stub implementation
-        associate(unused_real => data_min + upper_bound, &
-                  unused_arr => tick_positions, unused_int => num_ticks); end associate
+        real(wp) :: log_min, log_max, current_power
+        integer :: start_power, end_power, power
+        
+        if (data_min >= 0.0_wp .or. upper_bound >= 0.0_wp .or. upper_bound <= data_min) return
+        
+        ! Work with positive values for log calculations
+        ! For negative range [-500, -1], we want powers that give us ticks in that range
+        log_min = log10(-upper_bound)  ! log10(1) = 0 (closer to zero)
+        log_max = log10(-data_min)     ! log10(500) = ~2.7 (larger magnitude)
+        
+        start_power = floor(log_min)
+        end_power = ceiling(log_max)
 
-        ! Implementation for negative symlog region (placeholder)
+        do power = start_power, end_power
+            if (num_ticks >= MAX_TICKS) exit
+            current_power = -(10.0_wp**power)
+            
+            ! Check if tick is within bounds, excluding threshold boundary
+            if (current_power >= data_min - 1.0e-10_wp .and. &
+                current_power < upper_bound - 1.0e-10_wp) then
+                num_ticks = num_ticks + 1
+                tick_positions(num_ticks) = current_power
+            end if
+        end do
     end subroutine add_negative_symlog_ticks
 
     subroutine add_linear_symlog_ticks(lower_bound, upper_bound, tick_positions, num_ticks)
+        !! Add ticks for linear region of symlog scale
         real(wp), intent(in) :: lower_bound, upper_bound
         real(wp), intent(inout) :: tick_positions(MAX_TICKS)
         integer, intent(inout) :: num_ticks
 
-        ! Suppress unused parameter warnings for stub implementation
-        associate(unused_real => lower_bound + upper_bound, &
-                  unused_arr => tick_positions, unused_int => num_ticks); end associate
+        real(wp) :: range, step, tick_value
+        integer :: max_linear_ticks, i
+        
+        if (upper_bound <= lower_bound) return
+        
+        range = upper_bound - lower_bound
+        max_linear_ticks = 5  ! Reasonable number for linear region
+        
+        ! Always include zero if it's in the range
+        if (lower_bound <= 0.0_wp .and. upper_bound >= 0.0_wp .and. num_ticks < MAX_TICKS) then
+            num_ticks = num_ticks + 1
+            tick_positions(num_ticks) = 0.0_wp
+        end if
+        
+        ! Add additional linear ticks
+        step = range / real(max_linear_ticks + 1, wp)
+        step = calculate_nice_step(step)
 
-        ! Implementation for linear symlog region (placeholder)
+        ! Find first tick >= lower_bound
+        tick_value = ceiling(lower_bound / step) * step
+        
+        do while (tick_value <= upper_bound .and. num_ticks < MAX_TICKS)
+            ! Skip zero if already added, avoid duplicates
+            if (abs(tick_value) > 1.0e-10_wp) then
+                num_ticks = num_ticks + 1
+                tick_positions(num_ticks) = tick_value
+            end if
+            tick_value = tick_value + step
+        end do
     end subroutine add_linear_symlog_ticks
 
     subroutine add_positive_symlog_ticks(lower_bound, data_max, tick_positions, num_ticks)
+        !! Add ticks for positive logarithmic region of symlog scale
         real(wp), intent(in) :: lower_bound, data_max
         real(wp), intent(inout) :: tick_positions(MAX_TICKS)
         integer, intent(inout) :: num_ticks
 
-        ! Suppress unused parameter warnings for stub implementation
-        associate(unused_real => lower_bound + data_max, &
-                  unused_arr => tick_positions, unused_int => num_ticks); end associate
+        real(wp) :: log_min, log_max, current_power
+        integer :: start_power, end_power, power
+        
+        if (lower_bound <= 0.0_wp .or. data_max <= 0.0_wp) return
 
-        ! Implementation for positive symlog region (placeholder)
+        log_min = log10(lower_bound)
+        log_max = log10(data_max)
+        
+        start_power = floor(log_min)
+        end_power = ceiling(log_max)
+        
+        do power = start_power, end_power
+            if (num_ticks >= MAX_TICKS) exit
+            current_power = 10.0_wp**power
+            
+            ! Check if tick is within bounds, excluding threshold boundary
+            if (current_power > lower_bound + 1.0e-10_wp .and. &
+                current_power <= data_max + 1.0e-10_wp) then
+                num_ticks = num_ticks + 1
+                tick_positions(num_ticks) = current_power
+            end if
+        end do
     end subroutine add_positive_symlog_ticks
 
     function is_power_of_ten(value) result(is_power)

src/fortplot_rendering.f90

@@ -40,6 +40,11 @@ subroutine render_line_plot(backend, plot_data, plot_idx, x_min_t, x_max_t, y_mi
         real(wp), allocatable :: x_scaled(:), y_scaled(:)
         integer :: i, n
 
+        ! Validate input data
+        if (.not. allocated(plot_data%x) .or. .not. allocated(plot_data%y)) return
+        if (size(plot_data%x) == 0 .or. size(plot_data%y) == 0) return
+        if (size(plot_data%x) /= size(plot_data%y)) return
+        
         n = size(plot_data%x)
         allocate(x_scaled(n), y_scaled(n))
 
@@ -74,6 +79,11 @@ subroutine render_markers(backend, plot_data, x_min_t, x_max_t, y_min_t, y_max_t
         if (.not. allocated(plot_data%marker)) return
         if (len_trim(plot_data%marker) == 0) return
 
+        ! Validate input data
+        if (.not. allocated(plot_data%x) .or. .not. allocated(plot_data%y)) return
+        if (size(plot_data%x) == 0 .or. size(plot_data%y) == 0) return
+        if (size(plot_data%x) /= size(plot_data%y)) return
+        
         ! Draw markers
         call backend%color(plot_data%color(1), plot_data%color(2), plot_data%color(3))
 

test/test_character_bitmap_rendering.f90

@@ -2,8 +2,8 @@ program test_character_bitmap_rendering
     !! Unit test for verifying actual character bitmap rendering correctness
     !! Tests that characters are rendered with expected pixel patterns
     !! Backend-agnostic test that uses high-level rendering API
-    use fortplot_raster, only: render_text_to_bitmap
     use fortplot_text, only: init_text_system, cleanup_text_system, calculate_text_width, calculate_text_height
+    use fortplot_bitmap, only: render_text_to_bitmap
     implicit none
 
     logical :: all_tests_passed