Canvas and Viewport

Have you looked at the examples that come with RC? I am not sure if what you need is there I am away from my pc.

Sorry I missed the reply, does the beast demo use the canvases? I can't remember.

Sorry I am not much help, other then setting the main canvas I don't use them much in my game demos or my engine.

Here is a quick canvas example. Use the arrow keys to move around.

WindowOpen(0, "Canvas Demo", WINDOWPOS_CENTERED, WINDOWPOS_CENTERED, 640, 480, 0)

canvas_x = 100
canvas_y = 100

canvas_w = 640
canvas_h = 480

viewport_x = 0
viewport_y = 0

viewport_w = 100
viewport_h = 100


'This Canvas will fill the entire window
CanvasOpen(0, 640, 480, 0, 0, 640, 480, 0)
Canvas(0)
SetColor(RGB(0,255,0))

'This line will draw a box around the viewport of the canvas created below
Rect(canvas_x-1, canvas_y-1, viewport_w+2, viewport_h+2)



'This canvas will be the same size as canvas #0 but its viewport will only be 100 x 100
CanvasOpen(1, canvas_w, canvas_h, canvas_x, canvas_y, viewport_w, viewport_h, 0)
Canvas(1)
ClearCanvas

SetColor(RGB(0,0,255))
CircleFill(100, 100, 50)

'Set canvas #0 in the background
'Note: Canvases will be drawn in order from highest being in the background to lowest being in the foreground
'Canvas order can be from 0 (foreground) to 7 (background)
SetCanvasZ(0, 7)

'Set canvas #1 as the next canvas to be drawn after canvas # 0
SetCanvasZ(1, 6)

While Not Key(K_ESCAPE)
If Key(K_RIGHT) And (viewport_x+1) < canvas_w Then
viewport_x = viewport_x + 1
ElseIf Key(K_LEFT) And (viewport_x-1) >= 0 Then
viewport_x = viewport_x - 1
End If

If Key(K_DOWN) And (viewport_y+1) < canvas_h Then
viewport_y = viewport_y + 1
ElseIf Key(K_UP) And (viewport_y-1) >= 0 Then
viewport_y = viewport_y - 1
End If

'Move the offset of the canvas view
SetCanvasOffset(1, viewport_x, viewport_y)

Update
Wend


rosy I will try to explain how canvases work.

* A canvas is a drawing surface.
* The canvas can be as large as you want but only the viewport of the canvas will be visible in the window.
* The Location of the viewport ( viewport_x and viewport_y ) is where the viewport will be drawn in the window.

Refer to CanvasOpen() in the manual for how to set this up.

Look at this picture.


Even though the canvas above is a 600 x 400 drawing surface, the viewport is only a 200 x 200 area which is offset at (0, 0) which is the top left of the canvas.

Refer to SetCanvasOffset() in the manual for how to change the offset of the canvas.

Here is what that would look like when its drawn.



Here we are taking the same canvas and just changing the offset of where the viewport is looking at on the canvas. Notice the viewport is still in the same location in the window and the area of the canvas inside the viewport is what is changing.


And here is what the change in offset will draw on this image.

The manual is constantly evolving. johnno56 could tell you what the manual was like 5 years ago. It was a PDF file with a list of functions and almost no explanation for what they did. I make improvements to the manual with every release but it does take time.

SetCanvasViewport is not your problem. Your problem is SetCanvasOffset().

SetCanvasOffset() is setting where the viewport will look at your canvas from. If this is less than zero then your image will start to stretch because you are trying to draw a part of the image that doesn't exist. It will cause errors trying to draw if you set the offset where its trying to draw past the end of the image.

Try adding these if statements before you call SetCanvasViewport() or SetCanvasOffset() in your example:
   If (x1 + vx) >=  570 Then
x1 = 570 - vx
ElseIf x1 < 0 Then
x1 = 0
End If

If (y1 + vy) >=  420 Then
y1 = 420 - vy
ElseIf y1 < 0 Then
y1 = 0
End If

This code just makes sure x1 and y1 are never less than zero and they are never greater than the size of the canvas.

Basically if your viewport width is 370 and your canvas width is 570 then your x offset should never be greater than 200 -> ( 570 - 370 ).