Issue title: Huge lags caused by compton
 Issue body: // The template below is for reporting bugs. For feature requests and others, feel free to delete irrelevant entries.

### Platform
// Example: Ubuntu Desktop 17.04 amd64

Arch Linux

### GPU, drivers, and screen setup
// Example: NVidia GTX 670, nvidia-drivers 381.09, two monitors configured side-by-side with xrandr
// Please include the version of the video drivers (xf86-video-*) and mesa.
// Please also paste the output of `glxinfo -B` here.

HP Elitebook 8570p, Radeon HD 7550M/7570M/7650M, xf86-video-ati 1:19.0.1-1


```
name of display: :0
display: :0  screen: 0
direct rendering: Yes
Extended renderer info (GLX_MESA_query_renderer):
    Vendor: X.Org (0x1002)
    Device: AMD TURKS (DRM 2.50.0 / 4.19.44-1-lts, LLVM 8.0.0) (0x6841)
    Version: 19.0.4
    Accelerated: yes
    Video memory: 1024MB
    Unified memory: no
    Preferred profile: core (0x1)
    Max core profile version: 3.3
    Max compat profile version: 3.1
    Max GLES1 profile version: 1.1
    Max GLES[23] profile version: 3.1
Memory info (GL_ATI_meminfo):
    VBO free memory - total: 1023 MB, largest block: 1023 MB
    VBO free aux. memory - total: 1021 MB, largest block: 1021 MB
    Texture free memory - total: 1023 MB, largest block: 1023 MB
    Texture free aux. memory - total: 1021 MB, largest block: 1021 MB
    Renderbuffer free memory - total: 1023 MB, largest block: 1023 MB
    Renderbuffer free aux. memory - total: 1021 MB, largest block: 1021 MB
Memory info (GL_NVX_gpu_memory_info):
    Dedicated video memory: 1024 MB
    Total available memory: 2045 MB
    Currently available dedicated video memory: 1023 MB
OpenGL vendor string: X.Org
OpenGL renderer string: AMD TURKS (DRM 2.50.0 / 4.19.44-1-lts, LLVM 8.0.0)
OpenGL core profile version string: 3.3 (Core Profile) Mesa 19.0.4
OpenGL core profile shading language version string: 3.30
OpenGL core profile context flags: (none)
OpenGL core profile profile mask: core profile

OpenGL version string: 3.1 Mesa 19.0.4
OpenGL shading language version string: 1.40
OpenGL context flags: (none)

OpenGL ES profile version string: OpenGL ES 3.1 Mesa 19.0.4
OpenGL ES profile shading language version string: OpenGL ES GLSL ES 3.10
```


### Environment
// Tell us something about the desktop environment you are using, for example: i3-gaps, Gnome Shell, etc.
i3  version 4.16.1 (2019-01-27)

### Compton version
// Put the output of `compton --version` here.
// If you are running compton v4 or later, please also include the output of `compton --diagnostics`
// Example: v1

```
**Version:** v6.2

### Extensions:

* Shape: Yes
* XRandR: Yes
* Present: Present

### Misc:

* Use Overlay: Yes
* Config file used: /etc/xdg/compton.conf

```


### Compton configuration:
(default)

### Steps of reproduction
// If you can reliably reproduce this bug, please describe the quickest way to do so
// This information will greatly help us diagnosing and fixing the issue.

1. Launch i3
2. Launch compton
3. Launch telegram-desktop (Arch Linux package: telegram-desktop 1.7.0-1)
4. Minimize Telegram / change workspace / focus on another window
5. Have one of your friends type such that the string "typing..." appears in the top (with the animation)

### Expected behavior

Nothing

### Current Behavior

Entire computer starts lagging, as you type the text appears with a delay, any animation by any program (including compton's transition effect) lags, scrolling through webpages lags up to a second, YouTube becomes completely unusable etc.


 Comments: 
 Comment 0: Is there anything going on with the CPU usage?
 Comment 1: And does this happen with the `xrender` backend?
 Comment 2: Thanks for the fast reaction! CPU goes up to 10% which is normal.

It only happens with xrender backend. When using compton with glx, everything works normally.
 Comment 3: @kalsan Is 10% the whole system's CPU usage?

This might just be an example of xrender's poor performance. If `glx` works without problem I suggest you just stick with that.
 Comment 4:  Yes this is a good workaround for me. I'll leave the issue open since the actual bug remains.
{'source': 'GithubIssues', 'repo_name_with_owner': 'yshui/compton', 'issue_id': 445829712, 'repo_stars': 465.0}