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Comments on Why is the ground of my Dino game(in PDF) not moving and instead shrinking ?

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Why is the ground of my Dino game(in PDF) not moving and instead shrinking ?

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Ground not moving instead shrinking when a cactus is spawned I'm creating a Chrome Dino-style game inside a PDF using JavaScript form fields . The ground is implemented using two adjacent button widgets that should continuously scroll left to create an infinite ground effect.

Instead of moving left as expected, the ground appears to "shrink" or compress over time.

Relevant code:

var GROUND_W = 550;  // width of ground field
var GROUND_SPEED = CACTUS_SPEED;

var Ground_1   = this.getField("Ground_1");
var Ground_1_1 = this.getField("Ground_1_1");

function update_ground() {
    var gr1 = Ground_1.rect;
    gr1[0] -= GROUND_SPEED;
    gr1[2] -= GROUND_SPEED;
    Ground_1.rect = gr1;

    var gr2 = Ground_1_1.rect;
    gr2[0] -= GROUND_SPEED;
    gr2[2] -= GROUND_SPEED;
    Ground_1_1.rect = gr2;

    if (gr1[2] <= 30) {
        gr1[0] = gr2[2];
        gr1[2] = gr2[2] + GROUND_W;
        Ground_1.rect = gr1;
    }

    if (gr2[2] <= 30) {
        gr2[0] = gr1[2];
        gr2[2] = gr1[2] + GROUND_W;
        Ground_1_1.rect = gr2;
    }
}

The initial widget rectangles are:

Ground_1   : [30 449 580 469]
Ground_1_1 : [580 449 1130 469]

The intention is:

Both ground segments move left every tick.
When one segment completely leaves the screen, it should be repositioned immediately after the other segment.
The visible ground should maintain a constant width with no shrinking or gaps.

What could cause the ground to appear to shrink instead of simply translating left when a cactus is spawned ?

javascript pdf

posted 3 months ago

CC BY-SA 4.0

3mo ago by Karl Knechtel‭

Ted‭

-5 reputation 1 0 -3 1

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2 comment threads

Is the width of a "cactus" field the same as that of an "empty" field? (1 comment)

Debugging and expectations (1 comment)

Karl Knechtel‭ wrote 3 months ago · edited 3 months ago

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You say that the Ground_1 rectangle has the initial values [30 449 580 469]. In your own words, what do you expect these values to mean? Did you try to verify the meaning? How? In order for the rectangle to translate to the left, how should those values change (what should they become), logically? Is that what the code does? (Did you try to check the new values for the rectangle as update_ground is repeatedly called? How?)

Q&A sites, fundamentally, are about finding out information you didn't already have; not about getting someone else to examine a problem. Before asking the "why", please examine the "what" more carefully.

Please also keep in mind that we wouldn't be able to see the effect you describe to diagnose it; the "relevant" code is, yes, probably all that's relevant, but not enough for someone else to reproduce the issue.

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Comments on Why is the ground of my Dino game(in PDF) not moving and instead shrinking ?

Why is the ground of my Dino game(in PDF) not moving and instead shrinking ?

2 comment threads