write_gradient.json

The JSON file of the “Gradients in a line, in a circle, and read from a function” example. Five panels: a header that fades out, the same fade on the diagonal, a glow carried past its own circle so the corners fill, a blend that goes by way of a third colour, and a checkerboard whose colour is worked out from where each point stands, redder to the right and greener towards the top.

JSON 244 lines

This file is a request: an application sends it over the network to the server, which creates the PDF and sends it back. It makes the same page as the Rust and Python versions of this example. A request names every file it uses, never its content; the call carries the request and the files together. A font the server already holds, such as DejaVuSans, is named with nothing attached. Send the request to the address the API page gives.

The library cuts each panel out of the page and paints the gradient through the hole; the request fills a rectangle with the gradient as the colour it is filled with. The ink lands on the same dots either way. The library also writes each label at a stated height, where a request gives a block of words a rectangle instead, so every label's rectangle here is worked back from that height and is far wider than the words in it need.

What this example is for

A gradient is the cheapest way to make a flat page look as though somebody designed it: a header that fades out, a bar with some depth to it, a panel that is not simply a rectangle of one colour. It is also the thing most often faked with an image, and the fake shows the moment the page is printed or looked at closely.

What this example shows

Download the file The same example in Rust The same example in Python See what it creates 
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{
  "shadings": [
    {
      "name": "horizontal",
      "shading": {
        "axial": {
          "from": [70.0, 560.0],
          "to": [280.0, 560.0],
          "start": [0.85, 0.12, 0.12],
          "end": [0.12, 0.2, 0.8]
        }
      }
    },
    {
      "name": "diagonal",
      "shading": {
        "axial": {
          "from": [315.0, 490.0],
          "to": [525.0, 730.0],
          "start": [0.95, 0.8, 0.1],
          "end": [0.1, 0.55, 0.2]
        }
      }
    },
    {
      "name": "radial",
      "shading": {
        "radial": {
          "from": [175.0, 405.0, 0.0],
          "to": [175.0, 405.0, 105.0],
          "start": [1.0, 1.0, 1.0],
          "end": [0.1, 0.15, 0.45],
          "extend": [false, true]
        }
      }
    },
    {
      "name": "three_stops",
      "shading": {
        "axial": {
          "from": [315.0, 320.0],
          "to": [525.0, 320.0],
          "space": "rgb",
          "function": {
            "stitching": {
              "functions": [
                {
                  "exponential": {
                    "low": [0.85, 0.12, 0.12],
                    "high": [0.12, 0.6, 0.2]
                  }
                },
                {
                  "exponential": {
                    "low": [0.12, 0.6, 0.2],
                    "high": [0.12, 0.2, 0.8]
                  }
                }
              ],
              "bounds": [0.5],
              "encode": [[0.0, 1.0], [0.0, 1.0]]
            }
          }
        }
      }
    },
    {
      "name": "checkerboard",
      "shading": {
        "function_based": {
          "anti_alias": true,
          "domain": [[0.0, 1.0], [0.0, 1.0]],
          "matrix": [210.0, 0.0, 0.0, 170.0, 70.0, 100.0],
          "space": "rgb",
          "function": {
            "calculation": {
              "domain": [[0.0, 1.0], [0.0, 1.0]],
              "range": [[0.0, 1.0], [0.0, 1.0], [0.0, 1.0]],
              "program": [
                2, "copy", 8.0, "mul", "floor",
                "exch", 8.0, "mul", "floor",
                "add", "cvi", 2, "mod", 0, "ne",
                3, 1, "roll",
                0.2, 4, 3, "roll",
                [
                  0.45, "mul", 3, 1, "roll",
                  0.45, "mul", 3, 1, "roll",
                  0.45, "mul", 3, 1, "roll"
                ],
                "if"
              ]
            }
          }
        }
      }
    }
  ],
  "items": [
    {
      "type": "text",
      "rect": {
        "llx": 70.0,
        "lly": 770.0,
        "urx": 525.0,
        "ury": 791.6
      },
      "content": [
        "Gradients, and a colour read from a function"
      ],
      "font": "DejaVuSans",
      "font_size": 18.0
    },
    {
      "type": "rect",
      "rect": {
        "llx": 70.0,
        "lly": 560.0,
        "urx": 280.0,
        "ury": 730.0
      },
      "fill": {
        "shading": "horizontal"
      }
    },
    {
      "type": "text",
      "rect": {
        "llx": 70.0,
        "lly": 545.0,
        "urx": 280.0,
        "ury": 557.0
      },
      "content": [
        "Axial, two colours"
      ],
      "font": "DejaVuSans",
      "font_size": 10.0
    },
    {
      "type": "rect",
      "rect": {
        "llx": 315.0,
        "lly": 560.0,
        "urx": 525.0,
        "ury": 730.0
      },
      "fill": {
        "shading": "diagonal"
      }
    },
    {
      "type": "text",
      "rect": {
        "llx": 315.0,
        "lly": 545.0,
        "urx": 525.0,
        "ury": 557.0
      },
      "content": [
        "Axial, on the diagonal"
      ],
      "font": "DejaVuSans",
      "font_size": 10.0
    },
    {
      "type": "rect",
      "rect": {
        "llx": 70.0,
        "lly": 320.0,
        "urx": 280.0,
        "ury": 490.0
      },
      "fill": {
        "shading": "radial"
      }
    },
    {
      "type": "text",
      "rect": {
        "llx": 70.0,
        "lly": 305.0,
        "urx": 280.0,
        "ury": 317.0
      },
      "content": [
        "Radial, outer extended"
      ],
      "font": "DejaVuSans",
      "font_size": 10.0
    },
    {
      "type": "rect",
      "rect": {
        "llx": 315.0,
        "lly": 320.0,
        "urx": 525.0,
        "ury": 490.0
      },
      "fill": {
        "shading": "three_stops"
      }
    },
    {
      "type": "text",
      "rect": {
        "llx": 315.0,
        "lly": 305.0,
        "urx": 525.0,
        "ury": 317.0
      },
      "content": [
        "Axial, three stops"
      ],
      "font": "DejaVuSans",
      "font_size": 10.0
    },
    {
      "type": "rect",
      "rect": {
        "llx": 70.0,
        "lly": 100.0,
        "urx": 280.0,
        "ury": 270.0
      },
      "fill": {
        "shading": "checkerboard"
      }
    },
    {
      "type": "text",
      "rect": {
        "llx": 70.0,
        "lly": 85.0,
        "urx": 525.0,
        "ury": 97.0
      },
      "content": [
        "Function-based: a checkerboard on x and y at once, anti-aliasing asked for"
      ],
      "font": "DejaVuSans",
      "font_size": 10.0
    }
  ]
}