Function swipe

js/impress.js:657–732

( pct )

        // is the UI counterpart to this). It is a semi-internal API and intentionally not
        // documented in DOCUMENTATION.md.
        var swipe = function( pct ) {
            if ( Math.abs( pct ) > 1 ) {
                return;
            }

            // Prepare & execute the preStepLeave event
            var event = { target: activeStep, detail: {} };
            event.detail.swipe = pct;

            // Will be ignored within swipe animation, but just in case a plugin wants to read this,
            // humor them
            event.detail.transitionDuration = config.transitionDuration;
            var idx; // Needed by jshint
            if ( pct < 0 ) {
                idx = steps.indexOf( activeStep ) + 1;
                event.detail.next = idx < steps.length ? steps[ idx ] : steps[ 0 ];
                event.detail.reason = "next";
            } else if ( pct > 0 ) {
                idx = steps.indexOf( activeStep ) - 1;
                event.detail.next = idx >= 0 ? steps[ idx ] : steps[ steps.length - 1 ];
                event.detail.reason = "prev";
            } else {

                // No move
                return;
            }
            if ( execPreStepLeavePlugins( event ) === false ) {

                // If a preStepLeave plugin wants to abort the transition, don't animate a swipe
                // For stop, this is probably ok. For substep, the plugin it self might want to do
                // some animation, but that's not the current implementation.
                return false;
            }
            var nextElement = event.detail.next;

            var nextStep = stepsData[ "impress-" + nextElement.id ];

            // If the same step is re-selected, force computing window scaling,
            var nextScale = nextStep.scale * windowScale;
            var k = Math.abs( pct );

            var interpolatedStep = {
                translate: {
                    x: interpolate( currentState.translate.x, -nextStep.translate.x, k ),
                    y: interpolate( currentState.translate.y, -nextStep.translate.y, k ),
                    z: interpolate( currentState.translate.z, -nextStep.translate.z, k )
                },
                rotate: {
                    x: interpolate( currentState.rotate.x, -nextStep.rotate.x, k ),
                    y: interpolate( currentState.rotate.y, -nextStep.rotate.y, k ),
                    z: interpolate( currentState.rotate.z, -nextStep.rotate.z, k ),

                    // Unfortunately there's a discontinuity if rotation order changes. Nothing I
                    // can do about it?
                    order: k < 0.7 ? currentState.rotate.order : nextStep.rotate.order
                },
                scale: interpolate( currentState.scale * windowScale, nextScale, k )
            };