copying pixmap pieces

[r...@amalasoft.com]

Hi All

I hope you and yours are safe, well, and at home.

I'm playing around with pixmaps, pixel buffers and the like and can't seem to find a way to copy or capture a shaped region from an existing pixmap or pixel buffer.  The shape I need to copy would be irregular and not always the same thing, so a rectangle copy (by itself) doesn't suffice.  I can create a pixmap with the shape I want, and can locate it in the right position, but that's about it.  I don't want to modify the original (source) pixmap but I could make a wholesale copy of that if the necessary operation is destructive of course.

Any suggestions using just EV_* functions?

Thanks

R

[Karsten Heusser]

Maybe the following example is helpful.

Although the source (pixel_buffer_colored_radiation) has rectangular shape

its appearance on a target pixmap depends on its pixels' alpha values.

In this case one third of the pixmap is completely transparent white.

With the target pixmap set to 'copy mode' (target_pixmap.set_copy_mode)

- source pixmaps with pixel buffers and

- source pixel buffers

drawn onto the target look the same.

    target_pixmap.set_copy_mode -- Should be the default.

    target_pixmap.draw_sub_pixel_buffer (
        100, 100,
        pixel_buffer_colored_radiation,
        pixel_buffer_colored_radiation.area
    )
    target_pixmap.draw_pixmap (
        200, 200,
        pixel_buffer_colored_radiation.to_pixmap
    )

    pixel_buffer_colored_radiation: EV_PIXEL_BUFFER

            -- 100 x 100 pixel buffer with completely transparent parts.
            --
            -- Appearance:
            --
            --              OOOOOO
            --         OOOOOOOOOOOOOOOO            [r]ed
            --          OOOOOO r OOOOO             [g]reen
            --             OOOOOOOOOO              [b]lue
            --             OOOOOOOO                [a]lpha = 0 (full transparency)
            --        a     OOOOOO     a
            --                OO
            -- OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO
            -- OOOOOOOOOOOOOOO  OOOOOOOOOOOOOOO
            --  OOOOO g OOOOO    OOOOO b OOOOO
            --   OOOOOOOOOO   a    OOOOOOOOOO
            --     OOOOOOO          OOOOOOO
            --       OOOO            OOOO
            --         O              O
        local
            l_iterator: EV_PIXEL_BUFFER_ITERATOR
            l_brightness: INTEGER
        do
            create Result.make_with_pixmap (pixmap_colored_radiation)
            Result.lock
            l_iterator := Result.pixel_iterator

            from
                l_iterator.start
            until
                l_iterator.after
            loop
                l_brightness := (
                    l_iterator.item.red.to_integer_32 +
                    l_iterator.item.green.to_integer_32 +
                    l_iterator.item.blue.to_integer_32
                )

                if l_brightness > 500 then
                    l_iterator.item.set_alpha (0)
                            -- Could be much more elaborated
                            -- with e.g. transparency gradients.
                end

                l_iterator.forth
            end

            Result.unlock
        end

    pixmap_colored_radiation: EV_PIXMAP
            -- 100 x 100 radiation symbol with 3 different colors
            -- on white background.
            --
            -- Note: `pixel_buffer_colored_radiation' is a companion
            --       with total transparency instead of white.
            --
            --
            --              OOOOOO                 [w]hite
            --         OOOOOOOOOOOOOOOO            [r]ed
            --          OOOOOO r OOOOO             [g]reen
            --             OOOOOOOOOO              [b]lue
            --             OOOOOOOO                [a]lpha (not used)
            --        w     OOOOOO     w
            --                OO
            -- OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO
            -- OOOOOOOOOOOOOOO  OOOOOOOOOOOOOOO
            --  OOOOO g OOOOO    OOOOO b OOOOO
            --   OOOOOOOOOO   w    OOOOOOOOOO
            --     OOOOOOO          OOOOOOO
            --       OOOO            OOOO
            --         O              O
        local
            pi: REAL_32
            angle: REAL_32
        do
            create Result.make_with_size (100, 100)
                    -- Background is white by default.
            pi := 3.1416

            angle := -pi/3.0

            across 1 |..| 3 as cur loop
                angle := angle + pi/1.5

                inspect
                    cur.item
                when 1 then
                    Result.set_foreground_color (
                        create {EV_COLOR}.make_with_rgb (1.0, 0.0, 0.0)
                    )
                when 2 then
                    Result.set_foreground_color (
                        create {EV_COLOR}.make_with_rgb (0.0, 1.0, 0.0)
                    )
                when 3 then
                    Result.set_foreground_color (
                        create {EV_COLOR}.make_with_rgb (0.0, 0.0, 1.0)
                    )
                end

                Result.fill_pie_slice (0, 0, 100, 100, angle, pi/3.0)
            end -- across
        end

Best,

Karsten

[r...@amalasoft.com]

Hi Karsten

That looks like it might work.  Might have a chance to try it later today.

Of course, I was hoping for something like pixel_buffer.do_whatever_I_want, but ... :)

Thanks!

R

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