helimap
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map heliware
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JavaScript
/**
* @module ol/reproj
*/
import {
containsCoordinate,
createEmpty,
extend,
forEachCorner,
getCenter,
getHeight,
getTopLeft,
getWidth,
} from './extent.js';
import {createCanvasContext2D, releaseCanvas} from './dom.js';
import {getPointResolution, transform} from './proj.js';
import {solveLinearSystem} from './math.js';
let brokenDiagonalRendering_;
/**
* @type {Array<HTMLCanvasElement>}
*/
export const canvasPool = [];
/**
* This draws a small triangle into a canvas by setting the triangle as the clip region
* and then drawing a (too large) rectangle
*
* @param {CanvasRenderingContext2D} ctx The context in which to draw the triangle
* @param {number} u1 The x-coordinate of the second point. The first point is 0,0.
* @param {number} v1 The y-coordinate of the second point.
* @param {number} u2 The x-coordinate of the third point.
* @param {number} v2 The y-coordinate of the third point.
*/
function drawTestTriangle(ctx, u1, v1, u2, v2) {
ctx.beginPath();
ctx.moveTo(0, 0);
ctx.lineTo(u1, v1);
ctx.lineTo(u2, v2);
ctx.closePath();
ctx.save();
ctx.clip();
ctx.fillRect(0, 0, Math.max(u1, u2) + 1, Math.max(v1, v2));
ctx.restore();
}
/**
* Given the data from getImageData, see if the right values appear at the provided offset.
* Returns true if either the color or transparency is off
*
* @param {Uint8ClampedArray} data The data returned from getImageData
* @param {number} offset The pixel offset from the start of data.
* @return {boolean} true if the diagonal rendering is broken
*/
function verifyBrokenDiagonalRendering(data, offset) {
// the values ought to be close to the rgba(210, 0, 0, 0.75)
return (
Math.abs(data[offset * 4] - 210) > 2 ||
Math.abs(data[offset * 4 + 3] - 0.75 * 255) > 2
);
}
/**
* Determines if the current browser configuration can render triangular clip regions correctly.
* This value is cached so the function is only expensive the first time called.
* Firefox on Windows (as of now) does not if HWA is enabled. See https://bugzilla.mozilla.org/show_bug.cgi?id=1606976
* Chrome works, and everything seems to work on OSX and Android. This function caches the
* result. I suppose that it is conceivably possible that a browser might flip modes while the app is
* running, but lets hope not.
*
* @return {boolean} true if the Diagonal Rendering is broken.
*/
function isBrokenDiagonalRendering() {
if (brokenDiagonalRendering_ === undefined) {
const ctx = createCanvasContext2D(6, 6, canvasPool);
ctx.globalCompositeOperation = 'lighter';
ctx.fillStyle = 'rgba(210, 0, 0, 0.75)';
drawTestTriangle(ctx, 4, 5, 4, 0);
drawTestTriangle(ctx, 4, 5, 0, 5);
const data = ctx.getImageData(0, 0, 3, 3).data;
brokenDiagonalRendering_ =
verifyBrokenDiagonalRendering(data, 0) ||
verifyBrokenDiagonalRendering(data, 4) ||
verifyBrokenDiagonalRendering(data, 8);
releaseCanvas(ctx);
canvasPool.push(ctx.canvas);
}
return brokenDiagonalRendering_;
}
/**
* Calculates ideal resolution to use from the source in order to achieve
* pixel mapping as close as possible to 1:1 during reprojection.
* The resolution is calculated regardless of what resolutions
* are actually available in the dataset (TileGrid, Image, ...).
*
* @param {import("./proj/Projection.js").default} sourceProj Source projection.
* @param {import("./proj/Projection.js").default} targetProj Target projection.
* @param {import("./coordinate.js").Coordinate} targetCenter Target center.
* @param {number} targetResolution Target resolution.
* @return {number} The best resolution to use. Can be +-Infinity, NaN or 0.
*/
export function calculateSourceResolution(
sourceProj,
targetProj,
targetCenter,
targetResolution
) {
const sourceCenter = transform(targetCenter, targetProj, sourceProj);
// calculate the ideal resolution of the source data
let sourceResolution = getPointResolution(
targetProj,
targetResolution,
targetCenter
);
const targetMetersPerUnit = targetProj.getMetersPerUnit();
if (targetMetersPerUnit !== undefined) {
sourceResolution *= targetMetersPerUnit;
}
const sourceMetersPerUnit = sourceProj.getMetersPerUnit();
if (sourceMetersPerUnit !== undefined) {
sourceResolution /= sourceMetersPerUnit;
}
// Based on the projection properties, the point resolution at the specified
// coordinates may be slightly different. We need to reverse-compensate this
// in order to achieve optimal results.
const sourceExtent = sourceProj.getExtent();
if (!sourceExtent || containsCoordinate(sourceExtent, sourceCenter)) {
const compensationFactor =
getPointResolution(sourceProj, sourceResolution, sourceCenter) /
sourceResolution;
if (isFinite(compensationFactor) && compensationFactor > 0) {
sourceResolution /= compensationFactor;
}
}
return sourceResolution;
}
/**
* Calculates ideal resolution to use from the source in order to achieve
* pixel mapping as close as possible to 1:1 during reprojection.
* The resolution is calculated regardless of what resolutions
* are actually available in the dataset (TileGrid, Image, ...).
*
* @param {import("./proj/Projection.js").default} sourceProj Source projection.
* @param {import("./proj/Projection.js").default} targetProj Target projection.
* @param {import("./extent.js").Extent} targetExtent Target extent
* @param {number} targetResolution Target resolution.
* @return {number} The best resolution to use. Can be +-Infinity, NaN or 0.
*/
export function calculateSourceExtentResolution(
sourceProj,
targetProj,
targetExtent,
targetResolution
) {
const targetCenter = getCenter(targetExtent);
let sourceResolution = calculateSourceResolution(
sourceProj,
targetProj,
targetCenter,
targetResolution
);
if (!isFinite(sourceResolution) || sourceResolution <= 0) {
forEachCorner(targetExtent, function (corner) {
sourceResolution = calculateSourceResolution(
sourceProj,
targetProj,
corner,
targetResolution
);
return isFinite(sourceResolution) && sourceResolution > 0;
});
}
return sourceResolution;
}
/**
* @typedef {Object} ImageExtent
* @property {import("./extent.js").Extent} extent Extent.
* @property {HTMLCanvasElement|HTMLImageElement|HTMLVideoElement} image Image.
*/
/**
* Renders the source data into new canvas based on the triangulation.
*
* @param {number} width Width of the canvas.
* @param {number} height Height of the canvas.
* @param {number} pixelRatio Pixel ratio.
* @param {number} sourceResolution Source resolution.
* @param {import("./extent.js").Extent} sourceExtent Extent of the data source.
* @param {number} targetResolution Target resolution.
* @param {import("./extent.js").Extent} targetExtent Target extent.
* @param {import("./reproj/Triangulation.js").default} triangulation Calculated triangulation.
* @param {Array<ImageExtent>} sources Array of sources.
* @param {number} gutter Gutter of the sources.
* @param {boolean} [renderEdges] Render reprojection edges.
* @param {boolean} [interpolate] Use linear interpolation when resampling.
* @return {HTMLCanvasElement} Canvas with reprojected data.
*/
export function render(
width,
height,
pixelRatio,
sourceResolution,
sourceExtent,
targetResolution,
targetExtent,
triangulation,
sources,
gutter,
renderEdges,
interpolate
) {
const context = createCanvasContext2D(
Math.round(pixelRatio * width),
Math.round(pixelRatio * height),
canvasPool
);
if (!interpolate) {
context.imageSmoothingEnabled = false;
}
if (sources.length === 0) {
return context.canvas;
}
context.scale(pixelRatio, pixelRatio);
function pixelRound(value) {
return Math.round(value * pixelRatio) / pixelRatio;
}
context.globalCompositeOperation = 'lighter';
const sourceDataExtent = createEmpty();
sources.forEach(function (src, i, arr) {
extend(sourceDataExtent, src.extent);
});
const canvasWidthInUnits = getWidth(sourceDataExtent);
const canvasHeightInUnits = getHeight(sourceDataExtent);
const stitchContext = createCanvasContext2D(
Math.round((pixelRatio * canvasWidthInUnits) / sourceResolution),
Math.round((pixelRatio * canvasHeightInUnits) / sourceResolution),
canvasPool
);
if (!interpolate) {
stitchContext.imageSmoothingEnabled = false;
}
const stitchScale = pixelRatio / sourceResolution;
sources.forEach(function (src, i, arr) {
const xPos = src.extent[0] - sourceDataExtent[0];
const yPos = -(src.extent[3] - sourceDataExtent[3]);
const srcWidth = getWidth(src.extent);
const srcHeight = getHeight(src.extent);
// This test should never fail -- but it does. Need to find a fix the upstream condition
if (src.image.width > 0 && src.image.height > 0) {
stitchContext.drawImage(
src.image,
gutter,
gutter,
src.image.width - 2 * gutter,
src.image.height - 2 * gutter,
xPos * stitchScale,
yPos * stitchScale,
srcWidth * stitchScale,
srcHeight * stitchScale
);
}
});
const targetTopLeft = getTopLeft(targetExtent);
triangulation.getTriangles().forEach(function (triangle, i, arr) {
/* Calculate affine transform (src -> dst)
* Resulting matrix can be used to transform coordinate
* from `sourceProjection` to destination pixels.
*
* To optimize number of context calls and increase numerical stability,
* we also do the following operations:
* trans(-topLeftExtentCorner), scale(1 / targetResolution), scale(1, -1)
* here before solving the linear system so [ui, vi] are pixel coordinates.
*
* Src points: xi, yi
* Dst points: ui, vi
* Affine coefficients: aij
*
* | x0 y0 1 0 0 0 | |a00| |u0|
* | x1 y1 1 0 0 0 | |a01| |u1|
* | x2 y2 1 0 0 0 | x |a02| = |u2|
* | 0 0 0 x0 y0 1 | |a10| |v0|
* | 0 0 0 x1 y1 1 | |a11| |v1|
* | 0 0 0 x2 y2 1 | |a12| |v2|
*/
const source = triangle.source;
const target = triangle.target;
let x0 = source[0][0],
y0 = source[0][1];
let x1 = source[1][0],
y1 = source[1][1];
let x2 = source[2][0],
y2 = source[2][1];
// Make sure that everything is on pixel boundaries
const u0 = pixelRound((target[0][0] - targetTopLeft[0]) / targetResolution);
const v0 = pixelRound(
-(target[0][1] - targetTopLeft[1]) / targetResolution
);
const u1 = pixelRound((target[1][0] - targetTopLeft[0]) / targetResolution);
const v1 = pixelRound(
-(target[1][1] - targetTopLeft[1]) / targetResolution
);
const u2 = pixelRound((target[2][0] - targetTopLeft[0]) / targetResolution);
const v2 = pixelRound(
-(target[2][1] - targetTopLeft[1]) / targetResolution
);
// Shift all the source points to improve numerical stability
// of all the subsequent calculations. The [x0, y0] is used here.
// This is also used to simplify the linear system.
const sourceNumericalShiftX = x0;
const sourceNumericalShiftY = y0;
x0 = 0;
y0 = 0;
x1 -= sourceNumericalShiftX;
y1 -= sourceNumericalShiftY;
x2 -= sourceNumericalShiftX;
y2 -= sourceNumericalShiftY;
const augmentedMatrix = [
[x1, y1, 0, 0, u1 - u0],
[x2, y2, 0, 0, u2 - u0],
[0, 0, x1, y1, v1 - v0],
[0, 0, x2, y2, v2 - v0],
];
const affineCoefs = solveLinearSystem(augmentedMatrix);
if (!affineCoefs) {
return;
}
context.save();
context.beginPath();
if (isBrokenDiagonalRendering() || !interpolate) {
// Make sure that all lines are horizontal or vertical
context.moveTo(u1, v1);
// This is the diagonal line. Do it in 4 steps
const steps = 4;
const ud = u0 - u1;
const vd = v0 - v1;
for (let step = 0; step < steps; step++) {
// Go horizontally
context.lineTo(
u1 + pixelRound(((step + 1) * ud) / steps),
v1 + pixelRound((step * vd) / (steps - 1))
);
// Go vertically
if (step != steps - 1) {
context.lineTo(
u1 + pixelRound(((step + 1) * ud) / steps),
v1 + pixelRound(((step + 1) * vd) / (steps - 1))
);
}
}
// We are almost at u0r, v0r
context.lineTo(u2, v2);
} else {
context.moveTo(u1, v1);
context.lineTo(u0, v0);
context.lineTo(u2, v2);
}
context.clip();
context.transform(
affineCoefs[0],
affineCoefs[2],
affineCoefs[1],
affineCoefs[3],
u0,
v0
);
context.translate(
sourceDataExtent[0] - sourceNumericalShiftX,
sourceDataExtent[3] - sourceNumericalShiftY
);
context.scale(
sourceResolution / pixelRatio,
-sourceResolution / pixelRatio
);
context.drawImage(stitchContext.canvas, 0, 0);
context.restore();
});
releaseCanvas(stitchContext);
canvasPool.push(stitchContext.canvas);
if (renderEdges) {
context.save();
context.globalCompositeOperation = 'source-over';
context.strokeStyle = 'black';
context.lineWidth = 1;
triangulation.getTriangles().forEach(function (triangle, i, arr) {
const target = triangle.target;
const u0 = (target[0][0] - targetTopLeft[0]) / targetResolution;
const v0 = -(target[0][1] - targetTopLeft[1]) / targetResolution;
const u1 = (target[1][0] - targetTopLeft[0]) / targetResolution;
const v1 = -(target[1][1] - targetTopLeft[1]) / targetResolution;
const u2 = (target[2][0] - targetTopLeft[0]) / targetResolution;
const v2 = -(target[2][1] - targetTopLeft[1]) / targetResolution;
context.beginPath();
context.moveTo(u1, v1);
context.lineTo(u0, v0);
context.lineTo(u2, v2);
context.closePath();
context.stroke();
});
context.restore();
}
return context.canvas;
}