dmester / canvas-renderer Goto Github PK

Symptoms

The following exception is thrown:

RangeError [ERR_OUT_OF_RANGE]: The value of "value" is out of range. It must be >= 0 and <= 4294967295. Received -1109855489
    at checkInt (internal/buffer.js:35:11)
    at writeU_Int32BE (internal/buffer.js:623:3)
    at Buffer.writeUInt32BE (internal/buffer.js:636:10)
    at PngEncoder_writeTrueColorWithAlpha [as writeTrueColorWithAlpha] (F:\CanvasRenderer\lib\png\pngEncoder.js:79:24)
    at Canvas_toPng [as toPng] (F:\CanvasRenderer\lib\canvas.js:113:13)
    at Canvas_toDataURL [as toDataURL] (F:\CanvasRenderer\lib\canvas.js:131:20)
    at Object.<anonymous> (F:\CanvasRenderer\tests\trueColorTest.js:67:58)
    at Module._compile (internal/modules/cjs/loader.js:689:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:700:10)
    at Module.load (internal/modules/cjs/loader.js:599:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:538:12)
    at Function.Module._load (internal/modules/cjs/loader.js:530:3)
    at Function.Module.runMain (internal/modules/cjs/loader.js:742:12)
    at startup (internal/bootstrap/node.js:282:19)
    at bootstrapNodeJSCore (internal/bootstrap/node.js:743:3)

The exception is only thrown for images that contain more than 256 colors, where at least one color has a red channel value over 127.

This was reported in dmester/jdenticon#33.

Cause

When the reulting image contains more than 256 colors, it can no longer be represented as a PNG with a palette, but is instead saved as a true-color PNG. Node function Buffer.writeUInt32BE is used to write the color data to the PNG data stream. This function had a parameter called noAssert which essentially forced the value to an unsigned 32 bit integer, even when the value was a negative number.

In Node 10.x and later, noAssert has been removed, and the function will now instead throw an exception when a negative number is passed to the function. This was sometimes done by canvas-renderer when the red component of the color was larger than 127, since canvas-renderer handled both unsigned and signed integers as color values.

Solution

Convert all color functions to return signed integers as color values. Signed integers are prefered over unsigned integers since all bitwise operators in JS convert all operands to signed 32-bit integers.

Also replace Buffer.writeUInt32BE with Buffer.writeInt32BE.

please implement toDataURL method

https://developer.mozilla.org/en-US/docs/Web/API/HTMLCanvasElement/toDataURL