fix: restore PDF coordinate scaling (fixes #985)

- Independent X/Y scaling in PDF coordinate mapping
- Update coord context before mapping line/text
- Aligns data with axes/ticks; CI green

Closes #985.

Author: krystophny

src/backends/vector/fortplot_pdf.f90

@@ -98,7 +98,9 @@ subroutine draw_pdf_line(this, x1, y1, x2, y2)
         class(pdf_context), intent(inout) :: this
         real(wp), intent(in) :: x1, y1, x2, y2
         real(wp) :: pdf_x1, pdf_y1, pdf_x2, pdf_y2
-        
+        ! Ensure coordinate context reflects latest figure ranges and plot area
+        call this%update_coord_context()
+
         call normalize_to_pdf_coords(this%coord_ctx, x1, y1, pdf_x1, pdf_y1)
         call normalize_to_pdf_coords(this%coord_ctx, x2, y2, pdf_x2, pdf_y2)
         call this%stream_writer%draw_vector_line(pdf_x1, pdf_y1, pdf_x2, pdf_y2)
@@ -151,6 +153,8 @@ subroutine draw_pdf_text_wrapper(this, x, y, text)
         integer :: processed_len
 
         call process_latex_in_text(text, processed_text, processed_len)
+        ! Keep context in sync for text coordinate normalization as well
+        call this%update_coord_context()
         call normalize_to_pdf_coords(this%coord_ctx, x, y, pdf_x, pdf_y)
         call draw_mixed_font_text(this%core_ctx, pdf_x, pdf_y, processed_text(1:processed_len))
     end subroutine draw_pdf_text_wrapper

src/backends/vector/fortplot_pdf_coordinate.f90

@@ -39,49 +39,28 @@ subroutine normalize_to_pdf_coords(ctx, x, y, pdf_x, pdf_y)
         real(wp), intent(in) :: x, y
         real(wp), intent(out) :: pdf_x, pdf_y
         real(wp) :: x_range, y_range
-        real(wp) :: x_scale, y_scale, common_scale
-        real(wp) :: effective_width, effective_height
-        real(wp) :: x_offset, y_offset
+        real(wp) :: x_scale, y_scale
         real(wp), parameter :: EPSILON = 1.0e-10_wp
 
         ! Calculate data ranges with epsilon protection
         x_range = ctx%x_max - ctx%x_min
         y_range = ctx%y_max - ctx%y_min
 
-        ! Handle degenerate cases first
+        ! Handle degenerate cases first (center in plot area)
         if (abs(x_range) < EPSILON) then
             pdf_x = real(ctx%plot_area%left, wp) + real(ctx%plot_area%width, wp) * 0.5_wp
+        else
+            x_scale = real(ctx%plot_area%width, wp) / x_range
+            pdf_x = (x - ctx%x_min) * x_scale + real(ctx%plot_area%left, wp)
         end if
 
         if (abs(y_range) < EPSILON) then
-            pdf_y = real(ctx%plot_area%bottom, wp) + &
-                    real(ctx%plot_area%height, wp) * 0.5_wp
+            pdf_y = real(ctx%plot_area%bottom, wp) + real(ctx%plot_area%height, wp) * 0.5_wp
+        else
+            y_scale = real(ctx%plot_area%height, wp) / y_range
+            ! PDF coordinates: Y=0 at bottom, direct mapping
+            pdf_y = (y - ctx%y_min) * y_scale + real(ctx%plot_area%bottom, wp)
         end if
-        
-        if (abs(x_range) < EPSILON .or. abs(y_range) < EPSILON) return
-        
-        ! Calculate potential scales for each axis
-        x_scale = real(ctx%plot_area%width, wp) / x_range
-        y_scale = real(ctx%plot_area%height, wp) / y_range
-        
-        ! Use the smaller scale to preserve aspect ratio
-        common_scale = min(x_scale, y_scale)
-        
-        ! Calculate effective dimensions using common scale
-        effective_width = x_range * common_scale
-        effective_height = y_range * common_scale
-        
-        ! Center the plot within the plot area
-        x_offset = (real(ctx%plot_area%width, wp) - effective_width) * 0.5_wp
-        y_offset = (real(ctx%plot_area%height, wp) - effective_height) * 0.5_wp
-        
-        ! Transform coordinates with aspect ratio preservation
-        pdf_x = (x - ctx%x_min) * common_scale + &
-                real(ctx%plot_area%left, wp) + x_offset
-        
-        ! PDF coordinates: Y=0 at bottom, so transform data coordinates directly
-        pdf_y = (y - ctx%y_min) * common_scale + &
-                real(ctx%plot_area%bottom, wp) + y_offset
     end subroutine normalize_to_pdf_coords
 
     real(wp) function pdf_get_width_scale(ctx) result(scale)
@@ -247,52 +226,33 @@ end subroutine pdf_render_ylabel
     subroutine safe_coordinate_transform(x, y, x_min, x_max, y_min, y_max, &
                                         plot_left, plot_width, plot_bottom, plot_height, &
                                         pdf_x, pdf_y)
-        !! Safe coordinate transformation with aspect ratio preservation
-        !! Updated to maintain correct aspect ratios like normalize_to_pdf_coords
+        !! Safe coordinate transformation using independent x/y scales
         real(wp), intent(in) :: x, y
         real(wp), intent(in) :: x_min, x_max, y_min, y_max
         real(wp), intent(in) :: plot_left, plot_width, plot_bottom, plot_height
         real(wp), intent(out) :: pdf_x, pdf_y
         real(wp), parameter :: EPSILON = 1.0e-10_wp
         real(wp) :: x_range, y_range
-        real(wp) :: x_scale, y_scale, common_scale
-        real(wp) :: effective_width, effective_height
-        real(wp) :: x_offset, y_offset
+        real(wp) :: x_scale, y_scale
 
         ! Calculate ranges with epsilon protection
         x_range = x_max - x_min
         y_range = y_max - y_min
 
-        ! Handle degenerate cases
+        ! Handle degenerate cases by centering
         if (abs(x_range) < EPSILON) then
             pdf_x = plot_left + plot_width * 0.5_wp
+        else
+            x_scale = plot_width / x_range
+            pdf_x = (x - x_min) * x_scale + plot_left
         end if
 
         if (abs(y_range) < EPSILON) then
             pdf_y = plot_bottom + plot_height * 0.5_wp
+        else
+            y_scale = plot_height / y_range
+            pdf_y = (y - y_min) * y_scale + plot_bottom
         end if
-        
-        if (abs(x_range) < EPSILON .or. abs(y_range) < EPSILON) return
-        
-        ! Calculate potential scales for each axis
-        x_scale = plot_width / x_range
-        y_scale = plot_height / y_range
-        
-        ! Use the smaller scale to preserve aspect ratio
-        common_scale = min(x_scale, y_scale)
-        
-        ! Calculate effective dimensions using common scale
-        effective_width = x_range * common_scale
-        effective_height = y_range * common_scale
-        
-        ! Center the plot within the plot area
-        x_offset = (plot_width - effective_width) * 0.5_wp
-        y_offset = (plot_height - effective_height) * 0.5_wp
-        
-        ! Transform coordinates with aspect ratio preservation
-        pdf_x = (x - x_min) * common_scale + plot_left + x_offset
-        pdf_y = (y - y_min) * common_scale + plot_bottom + y_offset
-        
     end subroutine safe_coordinate_transform
 
-end module fortplot_pdf_coordinate
+end module fortplot_pdf_coordinate