Cactus Image Viewer

by Wassim Alhajomar (@wassimulator)

A small single file handmade image viewer written in C/C++.

Used libraries:

ImGui for the UI, stb_image for decoding, cute_files.h to manage directories on different platforms, and a custom OpenGL renderer.
Supported file extensions: PNG, JPG, JPEG, BMP, GIF

Features:

• Standalone executable.
• Scans folder of opened image and allows flipping through supported images within folder.
• Supports loading image files in the sorted order of the folder, can be optionally disabled to default to alphabetic.
• Support for unicode file names.
• Multithreaded file loading.
• image pan and zoom with fitting modes; to width or height.
• Pixel color inspector and a quick copy of HEX value to clipboad.
• Animated GIF support with play/pause and seek controls.
• Quick toggle between nearest-neighbor and linear filtering for pixelart images.
• Pixel grid.
• Customizable background color with support for checkerboard with custom colors.
• Drag and drop support to opening image files.
• Switches to turn individual RGB channels off and switch between premultiplied alpha and straight RGB.
• Keyboard controls to pan, zoom, flip through files and GIF controls.
• Customizable settings to save each image's zoom and pan locations within a session, or to reset image zoom and pan upon file change.

Usage:

• Opening a file:
  • Drag and drop image file into the viewer, if the file is supported it should load the file and read the folder contents of the file's directory.
  • CactusViewer also supports "Open With..." by choosing it as the program to open an image with.
  • You can also use the command line to open a file by typing: > CactusViewer.exe "path_to_file" (make sure you write the full path of the file!).
• Move the mouse to the buttom of the screen to view controls, click on "config" to see controls and change settings.

Building:

Windows:

using a MSVC developer terminal:

• run bgui.bat to compile ImGui to imgui_all.obj
• run b.bat to build the project, output in \bin

Remarks:

• Update 1.2.0 ditches SDL and includes Windows platform code, the whole viewer is now one file.
• Make sure you compile imgui_all.cpp to imgui_all.obj and place that in \bin first.
• When compiling the main viewer make sure you link toimgui_all.obj gdi32.lib opengl32.lib glu32.lib.
• For the sake of everyone's sanity, this repo has prebuilt binaries of all the above for Windows x64, I will provide other builds if I make any.

Limitation: CactusViewer decodes image files into memory and uploads them to the GPU using a single texture, a limitation here is posed when of the image's dimensions is larger than the maximum texture size of the respective GPU. According to https://feedback.wildfiregames.com/report/opengl/feature/GL_MAX_TEXTURE_SIZE: 44% of users have GPUs that support up to 16384 x 16384 textures and 46% of users have GPUs that support up to 8192 x 8192, the last 10% have 4096 x 4069 limits or less. These ranges cover regular image usage, including large files of up to 60 or 268 megapixel images respectively. So this likely won't be a problem to most use cases.

Possible imporovements:

Possible things to expand on, since I don't have that much time to spend on this project for now:

• Unlock the supported image resolutions sizes beyong maximum GPU texture sizes, to support images larger than 60MP or 268MP respectively.
• Decode images at lower resolutions at first and only decode full image upon zooming, to improve display speed of large files.
• Stream decoding GIF files to eliminate any load times (though it is already miniscule).
• Support for HEIF, TIFF, and some RAW formats, some of those require special codec.
• Rectangle selection and viewing of x,y,w,h values.
• Crop and rotate image, stb_image_write.h is already included and should be able to save the files, only the editing algorithms and UI need to be written.
• Providing an optional software renderer backend.