Distortion when moving across the screen sprite (Raspberry 4B))

[PavelUT]

This program moves the yellow rectangle over the blue background. At the same time, the rectangle is strongly distorted when moving.
Question. I have a bug in the code or is this a FreeBasic feature to overcome?
(My computer Raspberry 4B)

Code: Select all

ScreenRes 800, 600, 32,2
Screenset  1,0
Dim As Integer x = 0
    Color RGB(255, 128, 0), RGB(0, 0, 200) 
    Cls 
Do
    Cls
    Line (x, 80)-Step(63, 127), RGB(255, 255, 0), BF
    x += 3: If (x > 639) Then x = 0
     ScreenSync
     Flip 
Loop While Inkey = ""

sleep
end

[D.J.Peters]

Try this without sceensync does it solve the problem ?

Joshy

Code: Select all

ScreenRes 800, 600, 32,2
Screenset  1,0
Dim As Integer x = 0
Color RGB(255, 128, 0), RGB(0, 0, 200)
Do
  Cls
  Line (x, 80)-Step(63, 127), RGB(255, 255, 0), BF
  x += 3: If (x > 639) Then x = 0
  Flip : sleep 1
Loop While Inkey = ""
sleep

[PavelUT]

Hello dear D.J. Peters. I am very glad that you paid attention to my question.

[PavelUT]

Unfortunately no. With this change in the program, the rectangle moves across the screen very quickly, and the distortion is even greater.
As you may have guessed, I am interested in moving sprites in 800x600 mode and 32 bit color. And this is just a simple example of a problem.

[fxm]

Can you test this with a [ScreenLock ... ScreenUnlock] block, by locking instead of double buffering?

Code: Select all

ScreenRes 800, 600, 32
Dim As Integer x = 0
Color RGB(255, 128, 0), RGB(0, 0, 200)
Do
  Screenlock
  Cls
  Line (x, 80)-Step(63, 127), RGB(255, 255, 0), BF
  Screenunlock
  x += 3: If (x > 639) Then x = 0
  Sleep 20
Loop While Inkey = ""
Sleep

[caseih]

By "distortion" do you mean tearing? I can confirm your sample code does show tearing on my desktop Linux machine running X11 (and compiz composite manager). fxm's code shows no tearing, but has some flicker.

[PavelUT]

Yes it is. It is very strange. Refreshing the 640x480, 32 screen takes about 0.001 seconds. That is, at a screen refresh rate of 60 hertz (which is already enough for comfortable graphics reproduction), the background is redrawn in 1/15 of a second. The sprite is much faster. Despite this, incomprehensible distortions occur. What's the matter? I do not understand

[PavelUT]

fxm, nothing helps. I have tried many examples. With all screen modes. I get the impression that 32-bit 2D graphics in FreeBasic are not working without OpenGL and Direct X

[caseih]

Tearing is a common complaint with X11 on Linux. It's kind of the nature of the graphics server. It's asynchronous, so it's hard to get redraws to coincide with the refresh. There are ways of synchronizing the drawing to the refresh rate but it's complicated and tricky with X11. That's part of the reason why everyone is trying to move to Wayland. If the FB graphics library was ported to wayland everything would be a lot smoother.

Fortunately you have a lot of options. You can work with straight OpenGL. Or you could use a library like SDL, which uses a variety of backends to get the smoothest drawing and decent frame rates. SDL is nearly as simple as the built-in FB graphics library. Plus it has sprites.

[counting_pine]

What do these distortions look like? Can you provide a screenshot, or failing that, a photo of the screen?

[PavelUT]

Believe it or not, when photographing with a phone and pressing the PrtSc key, perfect rectangles are obtained. Your only chance to test is to repeat this program on a Linux computer.

[PavelUT]

Here we managed to photograph the distortion
[img]I can not insert a picture
[/img]

[SARG]

[img]I can not insert a picture
[/img]

You have to upload the image somewhere and then put the link between the tags.

[caseih]

He's seeing tearing, which is quite common on X11 on Linux. The top part of the rectangle appears sheared off (offset slightly) from the bottom part of the rectangle, and kind of flickers. The rectangle is being redrawn by FB while X11 is displaying it. This happens because X11 lacks a vertical sync signal. Also X11 is asynchronous, meaning you ask it do draw something and it returns immediately, and draws whenever it can. This was good for the low-powered graphics systems of ancient days, but does not work well for modern video and animation requirements. TThere's really no solution for X11, other than using OpenGL as a backend, which is what libraries like SDL can do. As much as I love X11and its flexibility and ability to operate over a network, there are some significant drawbacks to X11, and this is one of them. Wayland, by contrast, focuses on making everything silky smooth and completely synchronized with the refresh rate of the screen.

[PavelUT]

Thanks for the detailed answer. That is, it turns out that the better the computer, the worse the image ...
Means under Windows these distortions will not be? And here's what's strange. When x + 1 is changed, the distortion is minimal, at x + 3 it becomes very noticeable. What is very strange, what difference does it make to a video card driver?