Removed the endx and y local vars from the filled rect function

Added checks for the filled rect function
Added comments for the filled rect function

stage4/.vscode/tasks.json

@@ -8,6 +8,12 @@
             "type": "shell",
             "command": "make qemu",
             "problemMatcher": []
+        },
+        {
+            "label": "Build and QEMU (debug)",
+            "type": "shell",
+            "command": "make qemu-gdb",
+            "problemMatcher": []
         }
     ]
 }

stage4/bootasm2.S

@@ -257,13 +257,10 @@ cons_plot_pixel_end:
 #define recty          6
 #define rectx          4
 
-#define rectendx      -2
-#define rectendy      -4
-
 cons_draw_filled_rect:
     pushw   %bp
     movw    %sp, %bp
-    subw    $4, %sp    # Make room for our local variables in the stack
+    #subw    $4, %sp    # Make room for our local variables in the stack
     
     # Store existing register values to the stack so we can restore later
     pushw   %ax
@@ -273,15 +270,73 @@ cons_draw_filled_rect:
     pushw   %si
     pushw   %di
 
-cons_filled_rect_setup:
-    movw    rectwidth(%bp), %ax
-    add     rectx(%bp), %ax
-    movw    %ax, rectendx(%bp)
-    
-    movw    rectheight(%bp), %bx
-    add     recty(%bp), %bx
-    movw    %bx, rectendy(%bp)
+cons_filled_rect_check_x_dir:
+    movw    rectwidth(%bp), %ax             # Check if the user has entered a negative width value and swap the direction to a positive
+    cmpw    $0, %ax
+    jge     cons_filled_rect_check_y_dir
+    add     %ax, rectx(%bp)
+    neg     rectwidth(%bp)
 
+cons_filled_rect_check_y_dir:
+    movw    rectheight(%bp), %ax            # Check if the user has entered a negative height value and swap the direction to a pos
+    cmpw    $0, %ax
+    jge     cons_filled_rect_check_x_zero
+    add     %ax, recty(%bp)
+    neg     rectheight(%bp)    
+
+cons_filled_rect_check_x_zero:
+    movw    rectx(%bp), %ax                 # Check if the x value is a negative value, set it to 0 and figure out the offset so we
+    movw    $0, %bx                         # dont write to unwanted memory locations
+    cmpw    %bx, %ax
+    jge     cons_filled_rect_check_x_screenwidth        
+    movw    %bx, rectx(%bp)                 # Set to x 0
+    sub     %ax, %bx                        # get the distance from 0 to x
+    sub     %bx, rectwidth(%bp)             # take this away from the width
+    jmp     cons_filled_rect_check_width_screenwidth
+
+cons_filled_rect_check_x_screenwidth:    
+    movw    (screen_width), %bx             # Check if the x is outside of the view port, if so just end the call
+    cmpw    %bx, %ax                        # since it will never draw anything
+    jg      cons_filled_rect_loop_end    
+
+cons_filled_rect_check_width_screenwidth:        
+    add     rectwidth(%bp), %ax
+    movw    (screen_width), %bx             # Check if the width ends up outside of the view port
+    cmpw    %bx, %ax
+    jle     cons_filled_rect_check_y_zero
+    sub     %bx, %ax
+    sub     %ax, rectwidth(%bp)             # Remove the excess from the width value so we dont overflow memory
+    
+cons_filled_rect_check_y_zero:
+    movw    recty(%bp), %ax                 # Check if the y value is a negative value, set it to 0 and figure out the offset so we
+    movw    $0, %bx                         # dont write to unwanted memory locations
+    cmpw    %bx, %ax
+    jge     cons_filled_rect_check_y_screenheight
+    movw    %bx, recty(%bp)                 # Set to y 0
+    sub     %ax, %bx                        # get the distance from 0 to y
+    sub     %bx, rectheight(%bp)            # take this away from the height
+    jmp     cons_filled_rect_check_height_screenheight
+
+cons_filled_rect_check_y_screenheight:    
+    movw    (screen_height), %bx            # Check if the y is outside of the view port, if so just end the call
+    cmpw    %bx, %ax                        # since it will never draw anything
+    jg      cons_filled_rect_loop_end     
+
+cons_filled_rect_check_height_screenheight:        
+    add     rectheight(%bp), %ax
+    movw    (screen_height), %bx            # Check if the width ends up outside of the view port
+    cmpw    %bx, %ax
+    jle     cons_filled_rect_setup
+    sub     %bx, %ax
+    sub     %ax, rectheight(%bp)            # Remove the excess from the width value so we dont overflow memory
+
+cons_filled_rect_check_empty:
+    cmpw    $0, rectwidth(%bp)              # Check if the width or height is now zero, end the function if so
+    jle     cons_filled_rect_loop_end
+    cmpw    $0, rectheight(%bp)
+    jle     cons_filled_rect_loop_end
+
+cons_filled_rect_setup:
     movw    $0xA000, %bx             # Set the start of the video memory location
     movw    %bx, %es                 # Move that address into the "extra segment" es register
 
@@ -290,21 +345,21 @@ cons_filled_rect_setup:
     mul     %dx                          # does the (y * 320) part of our math            
     add     rectx(%bp), %ax              # Add the value of x to register ax
     movw    %ax, %si
-    lea     %es:(%si), %bx      # Move the value of ax into the si counter
+    lea     %es:(%si), %bx      # Load the memory address into the bx register
     
-    movw    rectheight(%bp), %si
+    movw    rectheight(%bp), %si    # Set the counter to our height which should be the number of lines to draw to
 
 cons_filled_rect_loop_start:    
-    movw    rectcolor(%bp), %ax    
-    movw    %bx, %di 
-    movw    rectwidth(%bp), %cx
-    cld
-    rep     stosb
+    movw    rectcolor(%bp), %ax    # Set the color byte for our rep
+    movw    %bx, %di               # move the memory location to the di counter 
+    movw    rectwidth(%bp), %cx    # Set cx to our width so the rep knows when to end
+    cld                            # Clear the direction flag so our rep counter inc's
+    rep     stosb                  # Run the stosb to copy bytes into the data segment til cx is 0
 
     movw    (screen_width), %cx
-    add     %cx, %bx
+    add     %cx, %bx               # Add 320 to our current y value for the next line
 
-    dec     %si
+    dec     %si                    # Dex the height counter til we hit 0
     jnz     cons_filled_rect_loop_start