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API for reading from Framebuffer #7

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API for reading from Framebuffer #7

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a4a142d
Add read_frame
petoknm Sep 4, 2018
fb04219
Impl Index for Framebuffer
Sep 5, 2018
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19 changes: 18 additions & 1 deletion src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -9,9 +9,10 @@ use libc::ioctl;
use std::error::Error;
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@Roysten Roysten Sep 9, 2018

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Could you give an example where you would want to read the frame? You have previously written it yourself, so why not keep this data stored somewhere?

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@petoknm petoknm Sep 9, 2018

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I have made my own display that is using SPI and I want to read the framebuffer and push it over SPI to the display. In my case the OS/applications are writing to the framebuffer and I'm just pushing it to the display.

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@vlisivka vlisivka Mar 6, 2019

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I want to make screenshot of the framebuffer (drawn by an another application), so I need this logic too.

use std::fmt;
use std::fs::{File, OpenOptions};
use std::io::Write;
use std::io::{Read, Write};
use std::os::unix::io::AsRawFd;
use std::path::Path;
use std::ops::Index;

use memmap::{Mmap, Protection};

Expand Down Expand Up @@ -201,6 +202,13 @@ impl Framebuffer {
.unwrap();
}

///Reads a frame from the Framebuffer.
pub fn read_frame(&self, frame: &mut Vec<u8>) {
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@Roysten Roysten Sep 9, 2018

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Using &mut Vec as parameter requires the user of this function to use a Vec, which will allocate the required memory to fit the entire frame. This means that after every read the user will have to call .clear() on the vector before being able to use the same vector for the next read. Also it would not be possible to only read a small part of the frame.

Wouldn't it be better to change it to:

pub fn read_frame(&self, frame: &mut [u8]) {

and then use .read_exact(frame) later on?

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@petoknm petoknm Sep 9, 2018

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For reading parts of the framebuffer I would suggest we implement Index<Range> so that people can read it any way they want, e.g. let v = fb[4096..8192].to_vec();.

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@petoknm petoknm Sep 9, 2018

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For reading the entire frame I wanted to use Vec to not have to deal with the size(preallocating memory in case of an array)... but I guess we could also solve this in terms of Index<Range> => let v = fb[..].to_vec(), let slice = fb[..], and maybe writing too using IndexMut.

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@petoknm petoknm Sep 9, 2018

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This would give the user the choice to do whatever they want with the returned slice

unsafe { self.frame.as_slice() }
.read_to_end(frame)
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@Roysten Roysten Sep 9, 2018

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.read_exact(frame)

.unwrap();
}

///Creates a FixScreeninfo struct and fills it using ioctl.
pub fn get_fix_screeninfo(device: &File) -> Result<FixScreeninfo, FramebufferError> {
let mut info: FixScreeninfo = Default::default();
Expand Down Expand Up @@ -252,3 +260,12 @@ impl Framebuffer {
}
}
}

impl Index<usize> for Framebuffer {
type Output = u8;

fn index(&self, index: usize) -> &u8 {
unsafe { self.frame.as_slice() }
.index(index)
}
}