fix: resolve axis label rendering issues (Issue #335)

BACKLOG.md

@@ -19,6 +19,9 @@
 **Infrastructure & Documentation Issues (Lower Priority)**
 - [ ] #323: Test - add edge case tests for PDF heatmap color validation
 - [ ] #324: Refactor - define epsilon constant for numerical comparisons
+- [ ] #342: Refactor - complete symlog tick generation implementation
+- [ ] #343: Refactor - extract label positioning constants
+- [ ] #344: Refactor - add format threshold constants in axes module
 
 ## DOING (Current Work)
 - [ ] #335: Fix - Axes wrong and no labels visible on scale_examples.html

src/fortplot_ascii.f90

@@ -309,6 +309,11 @@ subroutine output_to_terminal(this)
         if (allocated(this%xlabel_text)) then
             call print_centered_title(this%xlabel_text, this%plot_width)
         end if
+
+        ! Print ylabel (simple horizontal placement for now)
+        if (allocated(this%ylabel_text)) then
+            print '(A)', this%ylabel_text
+        end if
     end subroutine output_to_terminal
 
     subroutine output_to_file(this, unit)
@@ -339,6 +344,11 @@ subroutine output_to_file(this, unit)
         if (allocated(this%xlabel_text)) then
             call write_centered_title(unit, this%xlabel_text, this%plot_width)
         end if
+
+        ! Write ylabel to the left side of the plot if present
+        if (allocated(this%ylabel_text)) then
+            write(unit, '(A)') this%ylabel_text
+        end if
     end subroutine output_to_file
 
     integer function get_char_density(char)
@@ -871,6 +881,7 @@ subroutine ascii_draw_axes_and_labels(this, xscale, yscale, symlog_threshold, &
                                          title, xlabel, ylabel, &
                                          z_min, z_max, has_3d_plots)
         !! Draw axes and labels for ASCII backend
+        use fortplot_axes, only: compute_scale_ticks, format_tick_label, MAX_TICKS
         class(ascii_context), intent(inout) :: this
         character(len=*), intent(in) :: xscale, yscale
         real(wp), intent(in) :: symlog_threshold
@@ -880,6 +891,10 @@ subroutine ascii_draw_axes_and_labels(this, xscale, yscale, symlog_threshold, &
         logical, intent(in) :: has_3d_plots
 
         real(wp) :: label_x, label_y
+        real(wp) :: x_tick_positions(MAX_TICKS), y_tick_positions(MAX_TICKS)
+        integer :: num_x_ticks, num_y_ticks, i
+        character(len=50) :: tick_label
+        real(wp) :: tick_x, tick_y
 
         ! ASCII backend: explicitly set title and draw simple axes
         if (present(title)) then
@@ -892,6 +907,24 @@ subroutine ascii_draw_axes_and_labels(this, xscale, yscale, symlog_threshold, &
         call this%line(x_min, y_min, x_max, y_min)
         call this%line(x_min, y_min, x_min, y_max)
 
+        ! Generate tick marks and labels for ASCII
+        ! X-axis ticks (drawn as characters along bottom axis)
+        call compute_scale_ticks(xscale, x_min, x_max, symlog_threshold, x_tick_positions, num_x_ticks)
+        do i = 1, num_x_ticks
+            tick_x = x_tick_positions(i)
+            ! For ASCII, draw tick marks as characters in the text output
+            tick_label = format_tick_label(tick_x, xscale)
+            call this%text(tick_x, y_min - 0.05_wp * (y_max - y_min), trim(tick_label))
+        end do
+
+        ! Y-axis ticks (drawn as characters along left axis)
+        call compute_scale_ticks(yscale, y_min, y_max, symlog_threshold, y_tick_positions, num_y_ticks)
+        do i = 1, num_y_ticks
+            tick_y = y_tick_positions(i)
+            tick_label = format_tick_label(tick_y, yscale)
+            call this%text(x_min - 0.1_wp * (x_max - x_min), tick_y, trim(tick_label))
+        end do
+
         ! Store xlabel and ylabel for rendering outside the plot frame
         if (present(xlabel)) then
             if (allocated(xlabel)) then

src/fortplot_axes.f90

@@ -11,7 +11,7 @@ module fortplot_axes
     implicit none
 
     private
-    public :: compute_scale_ticks, format_tick_label
+    public :: compute_scale_ticks, format_tick_label, MAX_TICKS
 
     integer, parameter :: MAX_TICKS = 20
 
@@ -141,14 +141,33 @@ function format_tick_label(value, scale_type) result(label)
         real(wp), intent(in) :: value
         character(len=*), intent(in) :: scale_type
         character(len=20) :: label
+        real(wp) :: abs_value
 
-        if (abs(value) < 1.0e-10_wp) then
+        abs_value = abs(value)
+
+        if (abs_value < 1.0e-10_wp) then
             label = '0'
         else if (trim(scale_type) == 'log' .and. is_power_of_ten(value)) then
             label = format_power_of_ten(value)
+        else if (abs_value >= 1000.0_wp .or. abs_value < 0.01_wp) then
+            ! Use scientific notation for very large or very small values
+            write(label, '(ES10.2)') value
+            label = adjustl(label)
+        else if (abs_value >= 100.0_wp) then
+            ! No decimal places for values >= 100
+            write(label, '(F0.0)') value
+        else if (abs_value >= 10.0_wp) then
+            ! One decimal place for values >= 10
+            write(label, '(F0.1)') value
+        else if (abs_value >= 1.0_wp) then
+            ! Two decimal places for values >= 1
+            write(label, '(F0.2)') value
         else
-            write(label, '(G0)') value
+            ! Three decimal places for small values
+            write(label, '(F0.3)') value
         end if
+
+        label = adjustl(label)
     end function format_tick_label
 
 

src/fortplot_figure_core.f90

@@ -934,12 +934,10 @@ subroutine render_figure_axes(self)
                                                      self%title, self%xlabel, self%ylabel, &
                                                      0.0_wp, 0.0_wp, .false.)
         type is (ascii_context)
-            ! ASCII backend: explicitly set title and draw simple axes
-            if (allocated(self%title)) then
-                call backend%set_title(self%title)
-            end if
-            call self%backend%line(self%x_min, self%y_min, self%x_max, self%y_min)
-            call self%backend%line(self%x_min, self%y_min, self%x_min, self%y_max)
+            call backend%draw_axes_and_labels_backend(self%xscale, self%yscale, self%symlog_threshold, &
+                                                     self%x_min, self%x_max, self%y_min, self%y_max, &
+                                                     self%title, self%xlabel, self%ylabel, &
+                                                     0.0_wp, 0.0_wp, .false.)
         class default
             ! For other backends, use simple axes
             call self%backend%line(self%x_min, self%y_min, self%x_max, self%y_min)

src/fortplot_raster.f90

@@ -946,6 +946,8 @@ subroutine raster_draw_axes_and_labels(this, xscale, yscale, symlog_threshold, &
                                           title, xlabel, ylabel, &
                                           z_min, z_max, has_3d_plots)
         !! Draw axes and labels for raster backends
+        use fortplot_axes, only: compute_scale_ticks, format_tick_label, MAX_TICKS
+        use fortplot_text, only: calculate_text_width, calculate_text_height
         class(raster_context), intent(inout) :: this
         character(len=*), intent(in) :: xscale, yscale
         real(wp), intent(in) :: symlog_threshold
@@ -955,14 +957,84 @@ subroutine raster_draw_axes_and_labels(this, xscale, yscale, symlog_threshold, &
         logical, intent(in) :: has_3d_plots
 
         real(wp) :: label_x, label_y
+        real(wp) :: x_tick_positions(MAX_TICKS), y_tick_positions(MAX_TICKS)
+        integer :: num_x_ticks, num_y_ticks, i
+        character(len=50) :: tick_label
+        real(wp) :: tick_x, tick_y
+        integer :: tick_length  ! Tick length in pixels
+        integer :: px, py, text_width, text_height
+        real(wp) :: line_r, line_g, line_b
+        integer(1) :: text_r, text_g, text_b
+        real(wp) :: dummy_pattern(1)  ! Dummy pattern for solid lines
+        real(wp) :: pattern_dist  ! Pattern distance (mutable)
+        character(len=500) :: processed_text, escaped_text
+        integer :: processed_len
 
         ! Set color to black for axes and text
         call this%color(0.0_wp, 0.0_wp, 0.0_wp)
+        line_r = 0.0_wp; line_g = 0.0_wp; line_b = 0.0_wp  ! Black color for lines
+        text_r = 0; text_g = 0; text_b = 0  ! Black color for text
 
         ! Draw axes
         call this%line(x_min, y_min, x_max, y_min)
         call this%line(x_min, y_min, x_min, y_max)
 
+        ! Generate and draw tick marks and labels
+        tick_length = 5  ! Tick length in pixels
+
+        ! X-axis ticks
+        call compute_scale_ticks(xscale, x_min, x_max, symlog_threshold, x_tick_positions, num_x_ticks)
+        do i = 1, num_x_ticks
+            tick_x = x_tick_positions(i)
+            ! Transform tick position to pixel coordinates
+            px = int((tick_x - x_min) / (x_max - x_min) * real(this%plot_area%width, wp) + real(this%plot_area%left, wp))
+            py = this%plot_area%bottom + this%plot_area%height  ! Bottom of plot area
+
+            ! Draw tick mark down from axis
+            dummy_pattern = 0.0_wp
+            pattern_dist = 0.0_wp
+            call draw_styled_line(this%raster%image_data, this%width, this%height, &
+                                 real(px, wp), real(py, wp), real(px, wp), real(py + tick_length, wp), &
+                                 line_r, line_g, line_b, 1.0_wp, 'solid', dummy_pattern, 0, 0.0_wp, pattern_dist)
+
+            ! Draw tick label below tick mark
+            tick_label = format_tick_label(tick_x, xscale)
+            call process_latex_in_text(trim(tick_label), processed_text, processed_len)
+            call escape_unicode_for_raster(processed_text(1:processed_len), escaped_text)
+            text_width = calculate_text_width(trim(escaped_text))
+            ! Center the label horizontally under the tick
+            call render_text_to_image(this%raster%image_data, this%width, this%height, &
+                                    px - text_width/2, py + tick_length + 5, trim(escaped_text), text_r, text_g, text_b)
+        end do
+
+        ! Y-axis ticks
+        call compute_scale_ticks(yscale, y_min, y_max, symlog_threshold, y_tick_positions, num_y_ticks)
+        do i = 1, num_y_ticks
+            tick_y = y_tick_positions(i)
+            ! Transform tick position to pixel coordinates
+            px = this%plot_area%left  ! Left edge of plot area
+            py = int(real(this%plot_area%bottom + this%plot_area%height, wp) - &
+                    (tick_y - y_min) / (y_max - y_min) * real(this%plot_area%height, wp))
+
+            ! Draw tick mark to the left from axis
+            dummy_pattern = 0.0_wp
+            pattern_dist = 0.0_wp
+            call draw_styled_line(this%raster%image_data, this%width, this%height, &
+                                 real(px - tick_length, wp), real(py, wp), real(px, wp), real(py, wp), &
+                                 line_r, line_g, line_b, 1.0_wp, 'solid', dummy_pattern, 0, 0.0_wp, pattern_dist)
+
+            ! Draw tick label to the left of tick mark
+            tick_label = format_tick_label(tick_y, yscale)
+            call process_latex_in_text(trim(tick_label), processed_text, processed_len)
+            call escape_unicode_for_raster(processed_text(1:processed_len), escaped_text)
+            text_width = calculate_text_width(trim(escaped_text))
+            text_height = calculate_text_height(trim(escaped_text))
+            ! Right-align the label to the left of the tick
+            call render_text_to_image(this%raster%image_data, this%width, this%height, &
+                px - tick_length - text_width - 5, py - text_height/2, &
+                trim(escaped_text), text_r, text_g, text_b)
+        end do
+
         ! Draw title at top if present
         if (present(title)) then
             if (allocated(title)) then
@@ -972,23 +1044,32 @@ subroutine raster_draw_axes_and_labels(this, xscale, yscale, symlog_threshold, &
             end if
         end if
 
-        ! Draw xlabel centered below x-axis
+        ! Draw xlabel centered below x-axis (below tick labels)
         if (present(xlabel)) then
             if (allocated(xlabel)) then
-                label_x = (x_min + x_max) / 2.0_wp
-                label_y = y_min - 0.05_wp * (y_max - y_min)
-                call this%text(label_x, label_y, xlabel)
+                call process_latex_in_text(xlabel, processed_text, processed_len)
+                call escape_unicode_for_raster(processed_text(1:processed_len), escaped_text)
+                text_width = calculate_text_width(trim(escaped_text))
+                ! Center horizontally in plot area, position below tick labels
+                px = this%plot_area%left + this%plot_area%width / 2 - text_width / 2
+                py = this%plot_area%bottom + this%plot_area%height + 30  ! 30 pixels below plot area
+                call render_text_to_image(this%raster%image_data, this%width, this%height, &
+                                        px, py, trim(escaped_text), text_r, text_g, text_b)
             end if
         end if
 
-        ! Draw ylabel to the left of y-axis
+        ! Draw ylabel to the left of y-axis (rotated would be better, but for now horizontal)
         if (present(ylabel)) then
             if (allocated(ylabel)) then
-                ! For raster, ylabel needs special handling for rotation
-                ! For now, just place it horizontally
-                label_x = x_min - 0.1_wp * (x_max - x_min)
-                label_y = (y_min + y_max) / 2.0_wp
-                call this%text(label_x, label_y, ylabel)
+                call process_latex_in_text(ylabel, processed_text, processed_len)
+                call escape_unicode_for_raster(processed_text(1:processed_len), escaped_text)
+                text_width = calculate_text_width(trim(escaped_text))
+                text_height = calculate_text_height(trim(escaped_text))
+                ! Position to the left of plot area, centered vertically
+                px = 10  ! 10 pixels from left edge
+                py = this%plot_area%bottom + this%plot_area%height / 2 - text_height / 2
+                call render_text_to_image(this%raster%image_data, this%width, this%height, &
+                                        px, py, trim(escaped_text), text_r, text_g, text_b)
             end if
         end if
     end subroutine raster_draw_axes_and_labels

test/test_axes_labels_comprehensive.f90

@@ -0,0 +1,54 @@
+program test_axes_labels_comprehensive
+    !! Comprehensive test for Issue #335: Missing axis labels and tick marks
+    !! Tests that all axis text elements are properly rendered in both PNG and ASCII
+
+    use fortplot
+    implicit none
+
+    real(wp), dimension(6) :: x_data, y_linear, y_log
+    integer :: i
+
+    print *, "=== Comprehensive Axes Labels Test ==="
+
+    ! Generate test data
+    x_data = [(real(i, wp), i = 1, 6)]
+    y_linear = x_data * 2.0_wp + 1.0_wp              ! Linear: 3, 5, 7, 9, 11, 13
+    y_log = exp(x_data * 0.5_wp)                     ! Exponential for log scale
+
+    ! Test 1: Linear scale with all axis elements
+    print *, "Testing linear scale with comprehensive axis labeling..."
+    call figure()
+    call plot(x_data, y_linear)
+    call title('Linear Scale Test - All Elements')
+    call xlabel('Input Values (x)')
+    call ylabel('Linear Response (2x+1)')
+    call savefig('test_linear_axes_comprehensive.png')
+    call savefig('test_linear_axes_comprehensive.txt')
+
+    ! Test 2: Log scale with proper formatting
+    print *, "Testing log scale with scientific notation..."
+    call figure()
+    call plot(x_data, y_log)
+    call set_yscale('log')
+    call title('Log Scale Test - Scientific Labels')
+    call xlabel('Input Index')
+    call ylabel('Exponential Growth')
+    call savefig('test_log_axes_comprehensive.png')
+    call savefig('test_log_axes_comprehensive.txt')
+
+    print *, ""
+    print *, "VERIFICATION CHECKLIST:"
+    print *, "========================"
+    print *, "For each output file, verify:"
+    print *, "1. Title text is visible at top"
+    print *, "2. X-axis label appears below plot"
+    print *, "3. Y-axis label appears left of plot"
+    print *, "4. Tick marks are visible on axes"
+    print *, "5. Tick labels show numerical values"
+    print *, "6. Log scale uses appropriate notation"
+    print *, ""
+    print *, "Files created:"
+    print *, "- test_linear_axes_comprehensive.png/txt"
+    print *, "- test_log_axes_comprehensive.png/txt"
+
+end program test_axes_labels_comprehensive