1Correctness Testing 2=================== 3 4Skia correctness testing is primarily served by a tool named DM. 5This is a quickstart to building and running DM. 6 7<!--?prettify lang=sh?--> 8 9 python tools/git-sync-deps 10 bin/gn gen out/Debug 11 ninja -C out/Debug dm 12 out/Debug/dm -v -w dm_output 13 14When you run this, you may notice your CPU peg to 100% for a while, then taper 15off to 1 or 2 active cores as the run finishes. This is intentional. DM is 16very multithreaded, but some of the work, particularly GPU-backed work, is 17still forced to run on a single thread. You can use `--threads N` to limit DM to 18N threads if you like. This can sometimes be helpful on machines that have 19relatively more CPU available than RAM. 20 21As DM runs, you ought to see a giant spew of output that looks something like this. 22~~~ 23Skipping nonrendering: Don't understand 'nonrendering'. 24Skipping angle: Don't understand 'angle'. 25Skipping nvprmsaa4: Could not create a surface. 26492 srcs * 3 sinks + 382 tests == 1858 tasks 27 28( 25MB 1857) 1.36ms 8888 image mandrill_132x132_12x12.astc-5-subsets 29( 25MB 1856) 1.41ms 8888 image mandrill_132x132_6x6.astc-5-subsets 30( 25MB 1855) 1.35ms 8888 image mandrill_132x130_6x5.astc-5-subsets 31( 25MB 1854) 1.41ms 8888 image mandrill_132x130_12x10.astc-5-subsets 32( 25MB 1853) 151µs 8888 image mandrill_130x132_10x6.astc-5-subsets 33( 25MB 1852) 154µs 8888 image mandrill_130x130_5x5.astc-5-subsets 34 ... 35( 748MB 5) 9.43ms unit test GLInterfaceValidation 36( 748MB 4) 30.3ms unit test HalfFloatTextureTest 37( 748MB 3) 31.2ms unit test FloatingPointTextureTest 38( 748MB 2) 32.9ms unit test DeferredCanvas_GPU 39( 748MB 1) 49.4ms unit test ClipCache 40( 748MB 0) 37.2ms unit test Blur 41~~~ 42Do not panic. 43 44As you become more familiar with DM, this spew may be a bit annoying. If you 45remove -v from the command line, DM will spin its progress on a single line 46rather than print a new line for each status update. 47 48Don't worry about the "Skipping something: Here's why." lines at startup. DM 49supports many test configurations, which are not all appropriate for all 50machines. These lines are a sort of FYI, mostly in case DM can't run some 51configuration you might be expecting it to run. 52 53Don't worry about the "skps: Couldn't read skps." messages either, you won't 54have those by default and can do without them. If you wish to test with them 55too, you can download them separately. 56 57The next line is an overview of the work DM is about to do. 58~~~ 59492 srcs * 3 sinks + 382 tests == 1858 tasks 60~~~ 61 62DM has found 382 unit tests (code linked in from tests/), and 492 other drawing 63sources. These drawing sources may be GM integration tests (code linked in 64from gm/), image files (from `--images`, which defaults to "resources") or .skp 65files (from `--skps`, which defaults to "skps"). You can control the types of 66sources DM will use with `--src` (default, "tests gm image skp"). 67 68DM has found 3 usable ways to draw those 492 sources. This is controlled by 69`--config`. The defaults are operating system dependent. On Linux they are "8888 gl nonrendering". 70DM has skipped nonrendering leaving two usable configs: 718888 and gl. These two name different ways to draw using Skia: 72 73 - 8888: draw using the software backend into a 32-bit RGBA bitmap 74 - gl: draw using the OpenGL backend (Ganesh) into a 32-bit RGBA bitmap 75 76Sometimes DM calls these configs, sometimes sinks. Sorry. There are many 77possible configs but generally we pay most attention to 8888 and gl. 78 79DM always tries to draw all sources into all sinks, which is why we multiply 80492 by 3. The unit tests don't really fit into this source-sink model, so they 81stand alone. A couple thousand tasks is pretty normal. Let's look at the 82status line for one of those tasks. 83~~~ 84( 25MB 1857) 1.36ms 8888 image mandrill_132x132_12x12.astc-5-subsets 85 [1] [2] [3] [4] 86~~~ 87 88This status line tells us several things. 89 90 1. The maximum amount of memory DM had ever used was 25MB. Note this is a 91 high water mark, not the current memory usage. This is mostly useful for us 92 to track on our buildbots, some of which run perilously close to the system 93 memory limit. 94 95 2. The number of unfinished tasks, in this example there are 1857, either 96 currently running or waiting to run. We generally run one task per hardware 97 thread available, so on a typical laptop there are probably 4 or 8 running at 98 once. Sometimes the counts appear to show up out of order, particularly at DM 99 startup; it's harmless, and doesn't affect the correctness of the run. 100 101 3. Next, we see this task took 1.36 milliseconds to run. Generally, the 102 precision of this timer is around 1 microsecond. The time is purely there for 103 informational purposes, to make it easier for us to find slow tests. 104 105 4. The configuration and name of the test we ran. We drew the test 106 "mandrill_132x132_12x12.astc-5-subsets", which is an "image" source, into an 107 "8888" sink. 108 109When DM finishes running, you should find a directory with file named `dm.json`, 110and some nested directories filled with lots of images. 111~~~ 112$ ls dm_output 1138888 dm.json gl 114 115$ find dm_output -name '*.png' 116dm_output/8888/gm/3x3bitmaprect.png 117dm_output/8888/gm/aaclip.png 118dm_output/8888/gm/aarectmodes.png 119dm_output/8888/gm/alphagradients.png 120dm_output/8888/gm/arcofzorro.png 121dm_output/8888/gm/arithmode.png 122dm_output/8888/gm/astcbitmap.png 123dm_output/8888/gm/bezier_conic_effects.png 124dm_output/8888/gm/bezier_cubic_effects.png 125dm_output/8888/gm/bezier_quad_effects.png 126 ... 127~~~ 128 129The directories are nested first by sink type (`--config`), then by source type (`--src`). 130The image from the task we just looked at, "8888 image mandrill_132x132_12x12.astc-5-subsets", 131can be found at `dm_output/8888/image/mandrill_132x132_12x12.astc-5-subsets.png`. 132 133`dm.json` is used by our automated testing system, so you can ignore it if you 134like. It contains a listing of each test run and a checksum of the image 135generated for that run. 136 137### Detail <a name="digests"></a> 138Boring technical detail: The checksum is not a checksum of the 139.png file, but rather a checksum of the raw pixels used to create that .png. 140That means it is possible for two different configurations to produce 141the same exact .png, but have their checksums differ. 142 143Unit tests don't generally output anything but a status update when they pass. 144If a test fails, DM will print out its assertion failures, both at the time 145they happen and then again all together after everything is done running. 146These failures are also included in the `dm.json` file. 147 148DM has a simple facility to compare against the results of a previous run: 149 150<!--?prettify lang=sh?--> 151 152 ninja -C out/Debug dm 153 out/Debug/dm -w good 154 155 # do some work 156 157 ninja -C out/Debug dm 158 out/Debug/dm -r good -w bad 159 160When using `-r`, DM will display a failure for any test that didn't produce the 161same image as the `good` run. 162 163For anything fancier, I suggest using skdiff: 164 165<!--?prettify lang=sh?--> 166 167 ninja -C out/Debug dm 168 out/Debug/dm -w good 169 170 # do some work 171 172 ninja -C out/Debug dm 173 out/Debug/dm -w bad 174 175 ninja -C out/Debug skdiff 176 mkdir diff 177 out/Debug/skdiff good bad diff 178 179 # open diff/index.html in your web browser 180 181That's the basics of DM. DM supports many other modes and flags. Here are a 182few examples you might find handy. 183 184<!--?prettify lang=sh?--> 185 186 out/Debug/dm --help # Print all flags, their defaults, and a brief explanation of each. 187 out/Debug/dm --src tests # Run only unit tests. 188 out/Debug/dm --nocpu # Test only GPU-backed work. 189 out/Debug/dm --nogpu # Test only CPU-backed work. 190 out/Debug/dm --match blur # Run only work with "blur" in its name. 191 out/Debug/dm --dryRun # Don't really do anything, just print out what we'd do. 192 193
