refactor: split fortplot_raster.f90 to comply with file size limits

BACKLOG.md

@@ -15,10 +15,10 @@
 **User-Facing Issues (Medium Priority)**
 
 **Infrastructure & Documentation Issues (Lower Priority)**
-- [ ] #360: Refactor - split fortplot_raster.f90 to comply with file size limits
 - [ ] #355: Fix - First plot is empty
 
 ## DOING (Current Work)
+- [ ] #360: Refactor - split fortplot_raster.f90 to comply with file size limits
 
 ## BLOCKED (Infrastructure Issues)
 

src/fortplot_bitmap.f90

@@ -0,0 +1,151 @@
+module fortplot_bitmap
+    use iso_c_binding
+    use fortplot_text, only: render_text_to_image
+    use, intrinsic :: iso_fortran_env, only: wp => real64
+    implicit none
+
+    private
+    public :: initialize_white_background, composite_image, composite_bitmap_to_raster
+    public :: render_text_to_bitmap, rotate_bitmap_90_cw, rotate_bitmap_90_ccw
+
+contains
+
+    subroutine initialize_white_background(image_data, w, h)
+        integer(1), intent(out) :: image_data(:)
+        integer, intent(in) :: w, h
+        integer :: expected_size
+
+        ! Validate inputs
+        if (w <= 0 .or. h <= 0) return
+
+        expected_size = w * h * 3
+
+        ! Validate array size matches expected size
+        if (size(image_data) < expected_size) then
+            return
+        end if
+
+        ! Use intrinsic assignment to initialize entire array at once - safer
+        image_data = -1_1  ! White = 255 = -1 in signed byte
+
+    end subroutine initialize_white_background
+
+    subroutine composite_image(main_image, main_width, main_height, &
+                              overlay_image, overlay_width, overlay_height, dest_x, dest_y)
+        integer(1), intent(inout) :: main_image(*)
+        integer, intent(in) :: main_width, main_height
+        integer(1), intent(in) :: overlay_image(*)
+        integer, intent(in) :: overlay_width, overlay_height, dest_x, dest_y
+        integer :: x, y, src_idx, dst_idx, img_x, img_y
+
+        do y = 1, overlay_height
+            do x = 1, overlay_width
+                img_x = dest_x + x - 1
+                img_y = dest_y + y - 1
+
+                if (img_x >= 1 .and. img_x <= main_width .and. &
+                    img_y >= 1 .and. img_y <= main_height) then
+
+                    src_idx = ((y - 1) * overlay_width + (x - 1)) * 3 + 1
+                    dst_idx = ((img_y - 1) * main_width + (img_x - 1)) * 3 + 1
+
+                    if (overlay_image(src_idx) /= -1_1 .or. &
+                        overlay_image(src_idx+1) /= -1_1 .or. &
+                        overlay_image(src_idx+2) /= -1_1) then
+                        main_image(dst_idx:dst_idx+2) = overlay_image(src_idx:src_idx+2)
+                    end if
+                end if
+            end do
+        end do
+    end subroutine composite_image
+
+    subroutine composite_bitmap_to_raster(raster_buffer, raster_width, raster_height, &
+                                         bitmap, bitmap_width, bitmap_height, dest_x, dest_y)
+        !! Composite 3D RGB bitmap directly onto raster image buffer
+        integer(1), intent(inout) :: raster_buffer(*)
+        integer, intent(in) :: raster_width, raster_height
+        integer(1), intent(in) :: bitmap(:,:,:)
+        integer, intent(in) :: bitmap_width, bitmap_height, dest_x, dest_y
+        integer :: x, y, raster_x, raster_y, raster_idx
+
+        do y = 1, bitmap_height
+            do x = 1, bitmap_width
+                raster_x = dest_x + x - 1
+                raster_y = dest_y + y - 1
+
+                ! Check bounds
+                if (raster_x >= 1 .and. raster_x <= raster_width .and. &
+                    raster_y >= 1 .and. raster_y <= raster_height) then
+
+                    ! Skip white pixels (don't composite background)
+                    if (bitmap(x, y, 1) /= -1_1 .or. &
+                        bitmap(x, y, 2) /= -1_1 .or. &
+                        bitmap(x, y, 3) /= -1_1) then
+
+                        raster_idx = ((raster_y - 1) * raster_width + (raster_x - 1)) * 3 + 1
+                        raster_buffer(raster_idx)     = bitmap(x, y, 1)  ! R
+                        raster_buffer(raster_idx + 1) = bitmap(x, y, 2)  ! G
+                        raster_buffer(raster_idx + 2) = bitmap(x, y, 3)  ! B
+                    end if
+                end if
+            end do
+        end do
+    end subroutine composite_bitmap_to_raster
+
+    subroutine render_text_to_bitmap(bitmap, width, height, x, y, text)
+        !! Render text to RGB bitmap by using existing PNG rendering then converting
+        use fortplot_text, only: render_text_to_image
+        integer(1), intent(inout) :: bitmap(:,:,:)
+        integer, intent(in) :: width, height, x, y
+        character(len=*), intent(in) :: text
+
+        ! Create temporary PNG buffer for text rendering
+        integer(1), allocatable :: temp_buffer(:)
+        integer :: i, j, buf_idx
+
+        allocate(temp_buffer(width * height * 3))
+        call initialize_white_background(temp_buffer, width, height)
+        call render_text_to_image(temp_buffer, width, height, x, y, text, 0_1, 0_1, 0_1)
+
+        ! Convert PNG buffer to bitmap
+        do j = 1, height
+            do i = 1, width
+                buf_idx = ((j - 1) * width + (i - 1)) * 3 + 1
+                bitmap(i, j, 1) = temp_buffer(buf_idx)     ! R
+                bitmap(i, j, 2) = temp_buffer(buf_idx + 1) ! G  
+                bitmap(i, j, 3) = temp_buffer(buf_idx + 2) ! B
+            end do
+        end do
+
+        deallocate(temp_buffer)
+    end subroutine render_text_to_bitmap
+
+    subroutine rotate_bitmap_90_ccw(src_bitmap, dst_bitmap, src_width, src_height)
+        !! Rotate bitmap 90 degrees clockwise: (x,y) -> (y, src_width-x+1)
+        integer(1), intent(in) :: src_bitmap(:,:,:)
+        integer(1), intent(out) :: dst_bitmap(:,:,:)
+        integer, intent(in) :: src_width, src_height
+        integer :: i, j
+
+        do j = 1, src_height
+            do i = 1, src_width
+                dst_bitmap(j, src_width - i + 1, :) = src_bitmap(i, j, :)
+            end do
+        end do
+    end subroutine rotate_bitmap_90_ccw
+
+    subroutine rotate_bitmap_90_cw(src_bitmap, dst_bitmap, src_width, src_height)
+        !! Rotate bitmap 90 degrees counter-clockwise: (x,y) -> (src_height-y+1, x)
+        integer(1), intent(in) :: src_bitmap(:,:,:)
+        integer(1), intent(out) :: dst_bitmap(:,:,:)
+        integer, intent(in) :: src_width, src_height
+        integer :: i, j
+
+        do j = 1, src_height
+            do i = 1, src_width
+                dst_bitmap(src_height - j + 1, i, :) = src_bitmap(i, j, :)
+            end do
+        end do
+    end subroutine rotate_bitmap_90_cw
+
+end module fortplot_bitmap

src/fortplot_png_encoder.f90

@@ -0,0 +1,31 @@
+module fortplot_png_encoder
+    use, intrinsic :: iso_fortran_env, only: wp => real64
+    implicit none
+
+    private
+    public :: bitmap_to_png_buffer
+
+contains
+
+    subroutine bitmap_to_png_buffer(bitmap, width, height, buffer)
+        !! Convert 3D RGB bitmap to PNG buffer format with filter bytes
+        integer(1), intent(in) :: bitmap(:,:,:)
+        integer, intent(in) :: width, height
+        integer(1), intent(out) :: buffer(:)
+        integer :: i, j, buf_idx, row_start
+
+        ! PNG format: each row starts with filter byte (0 = no filter) followed by RGB data
+        do j = 1, height
+            row_start = (j - 1) * (1 + width * 3) + 1
+            buffer(row_start) = 0_1  ! PNG filter byte: 0 = no filter
+
+            do i = 1, width
+                buf_idx = row_start + 1 + (i - 1) * 3
+                buffer(buf_idx)     = bitmap(i, j, 1) ! R
+                buffer(buf_idx + 1) = bitmap(i, j, 2) ! G
+                buffer(buf_idx + 2) = bitmap(i, j, 3) ! B
+            end do
+        end do
+    end subroutine bitmap_to_png_buffer
+
+end module fortplot_png_encoder