melpomene/melpomene.js

/* Melpomene webcomic reader JS */
/* Version 1.0.0 - UNSTABLE */
/* CC-BY-NC-SA : https://git.aribaud.net/caribaud/melpomene/ */

//============
//  CONTROLS
//============

MOVE_NEXT = "ArrowRight"
MOVE_BACK = "ArrowLeft"
TOGGLE_FULLSCREEN = "F"
TOGGLE_PROGRESSBAR = "P"
TOGGLE_VIEW_MODE = "V"


//========================
//  NAVIGATION CONSTANTS
//========================

PAGE_TRANSITION_SPEED = "1.5s"
MOUSEWHELL_MIN_DELAY = 50
DELAY_BEFORE_HIDDING_CONTROLS = 4000;

//====================
//  STATES CONSTANTS
//====================

READER_FRAME = document.getElementById("reader-frame")
READER_CONTENT_FRAME = document.getElementById("reader-content-frame")
READER_PAGES = document.getElementById("reader-pages")
FOCUS_OVERLAY_HEIGHT = document.getElementById("focus-overlay-height")
FOCUS_OVERLAY_WIDTH = document.getElementById("focus-overlay-width")
HELP_CONTROLS = document.getElementById("help-controls")
PROGRESS_BAR_CONTAINER = document.getElementById("reader-progress-container")
PROGRESS_BAR = document.getElementById("reader-progress-bar")
PROGRESS_BAR_PAGES = document.getElementById("reader-progress-pages")

//===========================
//  STATES GLOBAL VARIABLES
//===========================

// The variable ZOOMS can either be defined by another JS file or contructed at init
if (typeof PAGES_ZOOMS == 'undefined') {
    PAGES_ZOOMS = null
}

CURRENT_ZOOM = 0
CURRENT_PAGE = 1
CURRENT_WIDTH = 0
CURRENT_HEIGHT = 0
CURRENT_X = 0
CURRENT_Y = 0

IS_PAGE_MODE = false
MOUSEWHELL_WAIT = false

// =============
//   UTILITIES
// =============

// Zooms utilites
// --------------

function loadZoomsFromImgTagsIfRequired(){
    
    // Zooms may be defined by another JS file
    if (PAGES_ZOOMS == null){
        
        PAGES_ZOOMS = []
        
        // parse the data-zooms of each img and and the page number info
        for (var i = 0; i < READER_PAGES.children.length; i++) {
            
            zooms_raw_data = READER_PAGES.children[i].dataset.zooms
            
            // ';' separates zooms data, ',' separates values
            // We add the page number (adding 1 because of indexing)
            zooms = zooms_raw_data.split(";").map(
                zoom => [i + 1].concat(
                    zoom.split(',').map(
                        value => parseFloat(value)
                    )
                )
            )
            
            PAGES_ZOOMS = PAGES_ZOOMS.concat(zooms)
        }
        
    }
    
}

function getFirstZoomOfPage(pageNumber){
   
    for (var zoom_idx = 0; zoom_idx < PAGES_ZOOMS.length; zoom_idx++){
        if (PAGES_ZOOMS[zoom_idx][0] == pageNumber) {
            return zoom_idx
        }
    }
}

function getLastZoomOfPage(pageNumber){
    let res = null
    
    for (var zoom_idx = 0; zoom_idx < PAGES_ZOOMS.length; zoom_idx++){
        if (PAGES_ZOOMS[zoom_idx][0] == pageNumber) {
            res = zoom_idx
        }
        
        if (res != null && PAGES_ZOOMS[zoom_idx][0] != pageNumber) {
            break
        }
    }
    
    return res
}

function getZoomCountForPage(pageNumber) {
    return PAGES_ZOOMS.filter(zoom => zoom[0] == pageNumber).length
}

function getCurrentZoomIndexForPage() {
    previousZoomsCount = PAGES_ZOOMS.filter(zoom => zoom[0] < CURRENT_PAGE).length
    return CURRENT_ZOOM - previousZoomsCount + 1
}

function getReadingProgressPercent() {
    progressPerPage = 1 / getPagesCount()
    
    if (IS_PAGE_MODE){
        return 100 * progressPerPage * CURRENT_PAGE
    }
    
    progressPerZoom = progressPerPage / getZoomCountForPage(CURRENT_PAGE)
    
    readingProgress = (CURRENT_PAGE - 1) * progressPerPage + getCurrentZoomIndexForPage() * progressPerZoom
    
    return 100 * readingProgress
}

function updateProgressBar(){
    PROGRESS_BAR.style.width = getReadingProgressPercent() + "%"
}

// Dimensions utilites
// -------------------

function getPagesCount() {
    return READER_PAGES.childElementCount
}

function pageOriginalHeight(pageNumber) {
    return READER_PAGES.children[pageNumber - 1].height
}

function pageOriginalWidth(pageNumber) {
    return READER_PAGES.children[pageNumber - 1].width
}

function readerFrameRatio() {
    return READER_CONTENT_FRAME.clientWidth / READER_CONTENT_FRAME.clientHeight
}

function pageRatio(pageNumber) {
    return READER_PAGES.children[pageNumber - 1].width / READER_PAGES.children[pageNumber - 1].height
}

function pageMaxHeight(){
    let max_height = 0
    
    for (var i = 0; i < READER_PAGES.children.length; i++) {
        if(READER_PAGES.children[i].height > max_height){
            max_height = READER_PAGES.children[i].height
        }
    }
    
    return max_height
}

function pageVerticalOffset(pageNumber) {
    return ( pageMaxHeight() - pageOriginalHeight(pageNumber) ) / 2
}

function previousPagesWidth(pageNumber) {
    // The width of all previous pages relative to the provided index
    
    let totalWidth = 0
    
    for (let idx = 0; idx < pageNumber - 1; idx++){
        totalWidth = totalWidth + READER_PAGES.children[idx].width
    }
    
    return totalWidth
}

// =========
//  ACTIONS
// =========

function initReader(){
    loadZoomsFromImgTagsIfRequired()
    moveReaderDisplayToZoom(0)
    
    // Smoothly show pictures when they intersect with the viewport
    let visibilityObserver = new IntersectionObserver((entries, observer) => {
        entries.forEach((entry) => {
            if (entry.isIntersecting) {
                entry.target.style.opacity = 1
                entry.target.style.visibility = "visible"
            } else {
                entry.target.style.opacity = 0
                entry.target.style.visibility = "hidden"
            }
        });
    }, { root: READER_CONTENT_FRAME, rootMargin: "-10px" });
    
    for (var i = 0; i < READER_PAGES.children.length; i++) {
        let img = READER_PAGES.children[i];
        visibilityObserver.observe(img)
        
        PROGRESS_BAR_PAGES.appendChild(document.createElement("div"))
    }
    
    READER_PAGES.style.display = "flex"
    
    setTimeout(() => {
        READER_PAGES.hidden = false
    }, "300")
    
    setTimeout(() => {
        HELP_CONTROLS.style.opacity = null;
        HELP_CONTROLS.style.transform = null;
    }, DELAY_BEFORE_HIDDING_CONTROLS)
}


function moveReaderDisplayToArea(pageNumber, width, height, posx, posy){
    
    // Align the top-left corner of the frame with the page
    READER_PAGES.style.transform = "translate(-" + previousPagesWidth(pageNumber) + "px, -" + pageVerticalOffset(pageNumber) + "px )"
    
    // Then move so the top-left point of the zoom match the frame top-left
    READER_PAGES.style.transform = "translate(" + (- posx) + "px, " + (-posy) + "px )" + READER_PAGES.style.transform
    
    // Then, scale so the zoom would fit the frame, and center the zoom
    if (width == 0){
        width = pageOriginalWidth(pageNumber)
    }
    
    if (height == 0){
        height = pageOriginalHeight(pageNumber)
    }
    
    zoomRatio = width / height
    
    if (readerFrameRatio() > zoomRatio) {
        // Frame wider than zoom => scale so heights are the same, offset on x
        var zoomToFrameScaleFactor = READER_CONTENT_FRAME.clientHeight / height
        
        READER_PAGES.style.transform = "scale(" + zoomToFrameScaleFactor + ")" + READER_PAGES.style.transform
        
        var scaledWidth = width * zoomToFrameScaleFactor
        var offset = (READER_CONTENT_FRAME.clientWidth - scaledWidth) / 2
        
        READER_PAGES.style.transform = "translateX(" + offset + "px)" + READER_PAGES.style.transform
        
        updateFocusByWidth(scaledWidth)
    } else {
        // Frame narower than zoom => scale so left/right match, offset on y
        var zoomToFrameScaleFactor = READER_CONTENT_FRAME.clientWidth / width 
        
        READER_PAGES.style.transform = "scale(" + zoomToFrameScaleFactor + ")" + READER_PAGES.style.transform
        
        var scaledHeight = height * zoomToFrameScaleFactor
        var offset = (READER_CONTENT_FRAME.clientHeight - scaledHeight) / 2
        
        READER_PAGES.style.transform = "translateY(" + offset + "px)" + READER_PAGES.style.transform
        
        updateFocusByHeight(scaledHeight)
    }
    
    CURRENT_PAGE = pageNumber
    CURRENT_WIDTH = width
    CURRENT_HEIGHT = height
    CURRENT_X = posx
    CURRENT_Y = posy
}

function refreshReaderDisplay() {
    moveReaderDisplayToArea(CURRENT_PAGE, CURRENT_WIDTH, CURRENT_HEIGHT, CURRENT_X, CURRENT_Y)
}

function moveReaderDisplayToPage(pageNumber) {
    moveReaderDisplayToArea(pageNumber, 0, 0, 0, 0)
}

function moveReaderDisplayToZoom(index) {
    
    moveReaderDisplayToArea(PAGES_ZOOMS[index][0], PAGES_ZOOMS[index][1], PAGES_ZOOMS[index][2], PAGES_ZOOMS[index][3], PAGES_ZOOMS[index][4])
    
    CURRENT_ZOOM = index
}

function updateFocusByWidth(width){
    FOCUS_OVERLAY_WIDTH.style.width = (width / READER_CONTENT_FRAME.clientWidth * 100) + "%"
    FOCUS_OVERLAY_HEIGHT.style.height = "100%"
}

function updateFocusByHeight(height){
    FOCUS_OVERLAY_WIDTH.style.width = "100%"
    FOCUS_OVERLAY_HEIGHT.style.height = (height / READER_CONTENT_FRAME.clientHeight * 100) + "%"
}

function toggleViewMode() {
    if (IS_PAGE_MODE){
        if (CURRENT_ZOOM != null){
            moveReaderDisplayToZoom(CURRENT_ZOOM)
        } else {
            moveReaderDisplayToZoom(getFirstZoomOfPage(CURRENT_PAGE))
        }
        IS_PAGE_MODE = false
    } else {
        moveReaderDisplayToPage(CURRENT_PAGE)
        IS_PAGE_MODE = true
    }
    
    updateProgressBar()
}

function moveReader(to_next) {
        
    if (IS_PAGE_MODE){
        if (to_next && CURRENT_PAGE < getPagesCount()) {
            moveReaderDisplayToPage(CURRENT_PAGE + 1)
            CURRENT_ZOOM = null
        }
        
        else if (!to_next && CURRENT_PAGE > 1) {
            moveReaderDisplayToPage(CURRENT_PAGE - 1)
            CURRENT_ZOOM = null
        }
    
    } else {
    
        if (to_next && CURRENT_ZOOM < PAGES_ZOOMS.length - 1) {
            moveReaderDisplayToZoom(CURRENT_ZOOM + 1)
        }
        
        else if (!to_next && CURRENT_ZOOM > 0) {
            moveReaderDisplayToZoom(CURRENT_ZOOM - 1)
        }
    }
    
    updateProgressBar()
    
}


// =============
//   CALLBACKS
// =============

function handleKeyPress(key){
    
    if (key == MOVE_NEXT) {
        moveReader(true)
    }
    
    else if (key == MOVE_BACK) {
        moveReader(false)
    }
    
    else if (key.toUpperCase() == TOGGLE_FULLSCREEN){
        if (document.fullscreenElement == null){
            READER_FRAME.requestFullscreen();
        } else {
            document.exitFullscreen();
        }
        
    }
    
    else if (key.toUpperCase() == TOGGLE_PROGRESSBAR){
        if (PROGRESS_BAR_CONTAINER.hidden == true) {
            PROGRESS_BAR_CONTAINER.hidden = false
        } else {
            PROGRESS_BAR_CONTAINER.hidden = true
        }
        refreshReaderDisplay();
    }
    
    else if (key.toUpperCase() == TOGGLE_VIEW_MODE) {
        toggleViewMode()
    }

}

function handleMouseWhell(deltaY){
    
    if (MOUSEWHELL_WAIT){
        return
    } else {
        MOUSEWHELL_WAIT = true
        setTimeout(() => {
            MOUSEWHELL_WAIT = false
        }, MOUSEWHELL_MIN_DELAY)
    }
    
    if (deltaY > 0) {
        moveReader(true, false)
    }
    
    else {
        moveReader(false, false)
    }
}

// ======
//  INIT
// ======

window.addEventListener("load", (event) => {
  initReader()
});

addEventListener("resize", (event) => {
    refreshReaderDisplay();
});

addEventListener("keydown", (event) => {
    handleKeyPress(event.key, event.shiftKey)
});

addEventListener("wheel", (event) => {
    handleMouseWhell(event.deltaY)
});