Hi everyone,I am Kushal K S V S. This summer, I've been working for FreeType as a part of
Google Summer of Code 2017. I am thrilled to present my project to everyone.
I've developed a Test Framework for FreeType's rendering output. This tool
enables the developer to compare the rendering output of a 'base' version
to a 'test' (developer) version of FreeType.
For the working of the Project, go through README in the 'Working Branch' link above.
My Summer at FreeType
1. Spent the first month going through the codebase and documentation thoroughly and getting
ready with the tools to implement the project.
My First objective was to generate bitmap images for given font / rendering mode / point size
/ dpi and to calculate MurmurHash3 checksums to compare the image data of the two glyphs
rendered using two version of FreeType.
Although I was able to generate and compare bitmaps for different versions of FreeType,
bitmaps turned out to be a bad image format because the images are uncompressed and are
of very big size.
The challenging part was to figure out the efficient way to take out the image data from
FT_Bitmap's buffer and write it to the image for LCD rendered glyphs.
2. Next, I switched to PNG's for storing the images using the library libpng. I had to write the
whole code again. This didn't take long because now I had idea how to render images
using FreeType.
I was running the code two times. Once to generate images for the 'base' version
and one for the 'test' version. Then I was reading from the PNG files to get the image data
and then compare the data to generate image(s) after adding effects.This had major
problems.
-- Too many image files.
-- Extra files for Murmur3Hash checksums.
-- Reading and Writing the PNG(s) again making the program in inefficient.
-- Huge amounts of memory was taken up by the program.
3. The solution to decrease memory usage and increase speed was to dynamically link the code
to the two versions of the library. This way, running the code once will
--compare two version's image data for all glyphs in the font.
--Add effects and generate all PNG(s) needed.
( These effects help the user visualise the pixel by pixel differences in the two images of the
same glyph rendered with two different versions of FreeType. )
4. But the number of PNG(s) was too high so my mentors came up with an idea of using CSS
Sprite Sheets. This fits all the images related to a glyph in one image. This reduced the
number of images four fold.
-- A challenge was to compare the images generated by the two versions if the dimensions
are different. I solved this by aligning the images with respect to a corner pixel and then
padding the smaller image with white pixels.
5. Next comes the part to generate HTML pages to list all the glyphs generated. This was done
using File IO functions in C. Listing was done using
-- Glyph Index
-- Glyph Name
-- Difference Metric
along with the sprite sheets.
To visualise the differences, I used CSS3 Animations and devised an interactive webpage.
6. At last all this was automated using shell script so that the user can simultaneously test for
various fonts / render modes / point sizes / dpi and for FreeType versions of his/her choice.
The challenging part was to organise all the files generated and to link all the files to one
HTML file so that all the glyphs can be examined from one page itself.
All the code to generate PNG(s) and HTML pages was written in ANSI C.
I had an awesome experience working with FreeType. I'd like to thank the FreeType community
and my mentors for giving all the guidance needed along the way. I am proud to be a part of the
FreeType community.
Testing and Debugging.
--Code is made readable and comments are added.
Note: There is a problem with the output in the chrome browse.
Memory leakages are being fixed.
Additional features are to be added.