JSON Models Example

JSON Models Example

Qt 5.6.0 Reference Documentation

Contents

JSON Model Loader

Loading the Models

Loading the Textures

Input Handling

JSON Models Example

The JSON Models Example demonstrates loading and displaying more than one JSON model and more than one texture 纹理. It also implements simple mouse input handling to allow rotating the scene 场景旋转 and zooming 变焦摄影 into it. 放大

JSON Model Loader

First we include a JSON model parser 解析器, which handles parsing the JSON models into our internal models:

Qt.include(“ThreeJSLoader.js”)

可以使用Tween.js做动画，https://github.com/sole/tween.js 这个库可以用来定义某个属性值子两个值之间的过渡，自动计算两个值之间的过渡。

The ThreeJSLoader.js includes a reimplementation 重实现 of theJSON parser in three.js, but we will not go into its implementation details. 细节我需要追究！

Loading the Models

First we need to initialize all array buffers 缓冲数组 for the models:

function initBuffers() {

modelOne.verticesVBO = gl.createBuffer();

modelOne.verticesVBO.name = “modelOne.verticesVBO”;

modelOne.normalsVBO = gl.createBuffer();

modelOne.normalsVBO.name = “modelOne.normalsVBO”;

modelOne.texCoordVBO = gl.createBuffer();

modelOne.texCoordVBO.name = “modelOne.texCoordVBO”;

modelOne.indexVBO = gl.createBuffer();

modelOne.indexVBO.name = “modelOne.indexVBO”;

modelTwo.verticesVBO = gl.createBuffer();
modelTwo.verticesVBO.name = "modelTwo.verticesVBO";
modelTwo.normalsVBO  = gl.createBuffer();
modelTwo.normalsVBO.name = "modelTwo.normalsVBO";
modelTwo.texCoordVBO = gl.createBuffer();
modelTwo.texCoordVBO.name = "modelTwo.texCoordVBO";
modelTwo.indexVBO    = gl.createBuffer();
modelTwo.indexVBO.name = "modelTwo.indexVBO";

...

Then we request the models to be loaded:

function loadJSONModels() {

// Load the first model

var request = new XMLHttpRequest(); // 异步请求

request.open(“GET”, “gold.json”); //获取模型数据

request.onreadystatechange = function () {

if (request.readyState === XMLHttpRequest.DONE) {

handleLoadedModel(JSON.parse(request.responseText));

}

}

request.send(); // 相应法搜回去

log(” XMLHttpRequest sent for model one”)

// Load the second model
var request2 = new XMLHttpRequest();
request2.open("GET", "woodbox.json");
request2.onreadystatechange = function () {
if (request2.readyState === XMLHttpRequest.DONE) {
handleLoadedModel(JSON.parse(request2.responseText));
}
}
request2.send();
log("   XMLHttpRequest sent for model two")
...

Then, when the load requests return, we handle the models:

function handleLoadedModel(jsonObj) {

log(“handleLoadedModel…”);

var modelData = parseJSON3DModel(jsonObj, “”);

if (modelOne.count === 0)
fillModel(modelData, modelOne);
else if (modelTwo.count === 0)
fillModel(modelData, modelTwo);
...

Each buffer is bound and filled with the data parsed from the json models:

function fillModel(modelData, model) {

log(” fillModel…”);

log(” “+model.verticesVBO.name);

gl.bindBuffer(gl.ARRAY_BUFFER, model.verticesVBO);

gl.bufferData(gl.ARRAY_BUFFER,

new Float32Array(modelData.vertices),

gl.STATIC_DRAW);

log(” “+model.normalsVBO.name);

if (isLogEnabled && stateDumpExt)

log(“GL STATE DUMP:\n”+stateDumpExt.getGLStateDump(stateDumpExt.DUMP_VERTEX_ATTRIB_ARRAYS_BIT || stateDumpExt.DUMP_VERTEX_ATTRIB_ARRAYS_CONTENTS_BIT));

gl.bindBuffer(gl.ARRAY_BUFFER, model.normalsVBO);
gl.bufferData(gl.ARRAY_BUFFER,
new Float32Array(modelData.normals),
gl.STATIC_DRAW);

log("   "+model.texCoordVBO.name);
gl.bindBuffer(gl.ARRAY_BUFFER, model.texCoordVBO);
gl.bufferData(gl.ARRAY_BUFFER,
new Float32Array(modelData.texCoords[0]),
gl.STATIC_DRAW);

log("   "+model.indexVBO.name);
gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, model.indexVBO);
gl.bufferData(gl.ELEMENT_ARRAY_BUFFER,
new Uint16Array(modelData.indices),
gl.STATIC_DRAW);

model.count = modelData.indices.length;
log("   ...fillModel");

}

Loading the Textures

First we create the TextureImage objects for each of the images we are going to load and register handlers for the imageLoaded and imageLoadingFailed signals. In the imageLoaded signal handlers we create the OpenGL textures:

function loadTextures() {

// Load the first texture

var goldImage = TextureImageFactory.newTexImage();

goldImage.name = “goldImage”;

goldImage.imageLoaded.connect(function() {

log(” creating model one texture”);

modelOneTexture = gl.createTexture();

modelOneTexture.name = “modelOneTexture”;

gl.bindTexture(gl.TEXTURE_2D, modelOneTexture);

gl.texImage2D(gl.TEXTURE_2D, // target

0, // level

gl.RGBA, // internalformat

gl.RGBA, // format

gl.UNSIGNED_BYTE, // type

goldImage); // pixels

gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR);

gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR_MIPMAP_NEAREST);

gl.generateMipmap(gl.TEXTURE_2D);

});

goldImage.imageLoadingFailed.connect(function() {

console.log(“Texture load FAILED, “+goldImage.errorString);

});

goldImage.src = “qrc:///gold.jpg”;

log(” texture one source set”)

// Load the second texture
var woodBoxImage = TextureImageFactory.newTexImage();
woodBoxImage.name = "woodBoxImage";
woodBoxImage.imageLoaded.connect(function() {
log("    creating model two texture");
modelTwoTexture = gl.createTexture();
modelTwoTexture.name = "modelTwoTexture";
gl.bindTexture(gl.TEXTURE_2D, modelTwoTexture);
gl.texImage2D(gl.TEXTURE_2D,    // target
0,                // level
gl.RGBA,          // internalformat
gl.RGBA,          // format
gl.UNSIGNED_BYTE, // type
woodBoxImage);    // pixels
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR_MIPMAP_NEAREST);
gl.generateMipmap(gl.TEXTURE_2D);
});
woodBoxImage.imageLoadingFailed.connect(function() {
console.log("Texture load FAILED, "+woodBoxImage.errorString);
});
woodBoxImage.src = "qrc:///woodbox.jpg";
log("   texture two source set")
...

Input Handling

First we add a MouseArea to fill the Canvas3D:

MouseArea {

anchors.fill: parent

…

Before adding some functionality on it, we need to add properties to the canvas with initial values set:

property double xRot: 0.0

property double yRot: 45.0

property double distance: 2.0

After that, we add rotation on mouse movement when the left mouse button is pressed:

onMouseXChanged: {

// Do not rotate if we don’t have previous value

if (previousY !== 0)

canvas3d.yRot += mouseY - previousY

previousY = mouseY

// Limit the rotation to -90…90 degrees

if (canvas3d.yRot > 90)

canvas3d.yRot = 90

if (canvas3d.yRot < -90)

canvas3d.yRot = -90

}

onMouseYChanged: {

// Do not rotate if we don’t have previous value

if (previousX !== 0)

canvas3d.xRot += mouseX - previousX

previousX = mouseX

// Wrap the rotation around

if (canvas3d.xRot > 180)

canvas3d.xRot -= 360

if (canvas3d.xRot < -180)

canvas3d.xRot += 360

}

onReleased: {

// Reset previous mouse positions to avoid rotation jumping

previousX = 0

previousY = 0

}

We need to keep the previous x and y values to avoid rotation jumping when the mouse button is released and pressed again. We store them in these properties:

property int previousY: 0

property int previousX: 0

Then we add zooming by mouse wheel:

onWheel: {

canvas3d.distance -= wheel.angleDelta.y / 1000.0

// Limit the distance to 0.5…10

if (canvas3d.distance < 0.5)

canvas3d.distance = 0.5

if (canvas3d.distance > 10)

canvas3d.distance = 10

}

These properties are then used in the JavaScript side when calculating eye/camera movement:

// Get the view matrix

mat4.identity(vMatrix);

eye = moveEye(canvas.xRot, canvas.yRot, canvas.distance);

mat4.lookAt(vMatrix, eye, [0, 0, 0], [0, 1, 0]);

Converting the rotation values into movement is done as follows:

function moveEye(xRot, yRot, distance) {

var xAngle = degToRad(xRot);

var yAngle = degToRad(yRot);

var zPos = distance * Math.cos(xAngle) * Math.cos(yAngle);
var xPos = distance * Math.sin(xAngle) * Math.cos(yAngle);
var yPos = distance * Math.sin(yAngle);

return [-xPos, yPos, zPos];

}

Files:

canvas3d/jsonmodels/qml/jsonmodels/jsonmodels.js

canvas3d/jsonmodels/qml/jsonmodels/jsonmodels.qml

canvas3d/jsonmodels/main.cpp

canvas3d/jsonmodels/jsonmodels.pro

canvas3d/jsonmodels/qml.qrc