dualfroz
f78554106d
RgbToHex emitted a single hex digit for channel values below 0x10 because strconv.FormatInt produces the minimal representation. This broke the fixed-width hex format, the round-trip with HexToRgb, and the hex2basicMap fast path in Rgb2basic. Format each channel with %02x, matching RgbTo256.
72 lines
2.1 KiB
Markdown
72 lines
2.1 KiB
Markdown
# fix(convert): zero-pad each channel in RgbToHex
|
|
|
|
## Problem
|
|
|
|
`RgbToHex` (and its alias `Rgb2hex`) does not zero-pad channel values below
|
|
`0x10`, so a single hex digit is emitted for those channels:
|
|
|
|
```go
|
|
color.RgbToHex([]int{1, 2, 3}) // "123" , want "010203"
|
|
color.RgbToHex([]int{0, 0, 0}) // "000" , want "000000"
|
|
color.RgbToHex([]int{10, 11, 12}) // "0a0b0c" -> actually "abc"
|
|
```
|
|
|
|
This breaks two contracts:
|
|
|
|
1. The round-trip with `HexToRgb` is no longer an identity for colors with any
|
|
channel below 16:
|
|
|
|
```go
|
|
color.RgbToHex(color.HexToRgb("010203")) // "123", not "010203"
|
|
```
|
|
|
|
2. `Rgb2basic` looks a color up in `hex2basicMap`, whose keys are all
|
|
fixed-width 6-digit hex strings (e.g. "000000"). Because `RgbToHex(0,0,0)`
|
|
returns "000", pure black never matches the fast-path map and silently falls
|
|
through to the approximate `RgbToAnsi`.
|
|
|
|
The sibling converter `RgbTo256` already builds its hex key with
|
|
`fmt.Sprintf("%02x%02x%02x", ...)`, so this is an inconsistency within the same
|
|
file.
|
|
|
|
## Root cause
|
|
|
|
`convert.go`, `RgbToHex`:
|
|
|
|
```go
|
|
for _, v := range rgb {
|
|
hexNodes = append(hexNodes, strconv.FormatInt(int64(v), 16))
|
|
}
|
|
```
|
|
|
|
`strconv.FormatInt(_, 16)` produces the minimal representation, i.e. one digit
|
|
for values 0-15.
|
|
|
|
## Fix
|
|
|
|
Format each channel as a fixed two-digit hex value:
|
|
|
|
```go
|
|
hexNodes = append(hexNodes, fmt.Sprintf("%02x", v))
|
|
```
|
|
|
|
`fmt` is already imported in the file. Existing values >= 16 are unchanged.
|
|
|
|
## Test
|
|
|
|
Extended `TestRgbToHex` in `utils_test.go` with small-channel cases
|
|
(`{0,0,0}`, `{1,2,3}`, `{10,11,12}`) and an explicit
|
|
`RgbToHex(HexToRgb(hex)) == hex` round-trip check.
|
|
|
|
- Gate: `go test ./` -> ok (PASS)
|
|
- `go vet ./...` -> exit 0
|
|
- `go build ./...` -> exit 0
|
|
|
|
Counterfactual: reverting `RgbToHex` to `strconv.FormatInt(int64(v), 16)` makes
|
|
the new test fail with `expect: "abc"` vs `actual: "0a0b0c"`.
|
|
|
|
Note: `gofmt -l convert.go` reports the file, but this is pre-existing (a doc
|
|
comment near line 866, unrelated to this change and present on the base commit).
|
|
The changed region is gofmt-clean, so unrelated lines were intentionally left
|
|
untouched.
|