[textures] `ImageDraw()` rectangle clipping doesn't look right

[mattj1]

I was recently using ImageDraw and passing negative coordinates for the destination rectangle, which resulted in some graphical glitches.

Shouldn't this say srcRec.x -= dstRec.x; ? Line 3366 would be updated accordingly as well.

raylib/src/rtextures.c

Line 3358 in 5ed83df

srcRec.x = -dstRec.x;

I tried pre-clipping the coordinates, such that dstRec.X was never negative, before calling ImageDraw which fixed it for me.

[raysan5]

@mattj1 I think that function was reviewed recently but I didn't test the new behaviour, feel free to send a PR if you detected some issue and got a fix.

[raysan5]

@mattj1 Tested this issue with textures_image_drawing example and it seems work ok now. Feel free to reopen it if problem persist. Please, if you reopen it would help to provide some test code and some image of the error.

[mattj1]

Hi @raysan5 ,

I replaced the code of the demo you mentioned with the following.

The glitch only seems to happen if resizing wasn't necessary.

This example animates both as they get cropped off of the left side of the destination image.

#include "raylib.h"

//------------------------------------------------------------------------------------
// Program main entry point
//------------------------------------------------------------------------------------
int main(void)
{
    // Initialization
    //--------------------------------------------------------------------------------------
    const int screenWidth = 800;
    const int screenHeight = 450;

    InitWindow(screenWidth, screenHeight, "raylib [textures] example - image drawing");

    Image canvas = GenImageColor(700, 350, WHITE);

    Image parrots = LoadImage("resources/parrots.png");     // Load image in CPU memory (RAM)

    SetTargetFPS(30);
    //---------------------------------------------------------------------------------------

    int x = 50;

    // Main game loop
    while (!WindowShouldClose())    // Detect window close button or ESC key
    {
        x -= 1;
        if (x < -32) x = 50;

        // Update
        //----------------------------------------------------------------------------------
        // TODO: Update your variables here
        //----------------------------------------------------------------------------------

        // Draw
        //----------------------------------------------------------------------------------

        ImageClearBackground(&canvas, WHITE);




        // No scaling (glitch)
        ImageDraw(&canvas, parrots, (Rectangle){ 64, 64, 128, 128}, (Rectangle){ x, 32, 128, 128}, WHITE);

        // Scaling (works as expected)
        ImageDraw(&canvas, parrots, (Rectangle){ 64, 64, 128, 128}, (Rectangle){ x, 150, 150, 150}, WHITE);





        Texture2D canvasTexture = LoadTextureFromImage(canvas);
        BeginDrawing();
            ClearBackground(RAYWHITE);
            DrawTexture(canvasTexture, screenWidth/2 - canvasTexture.width/2, screenHeight/2 - canvasTexture.height/2 - 40, WHITE);
        EndDrawing();
        UnloadTexture(canvasTexture);
        //----------------------------------------------------------------------------------
    }

    // De-Initialization
    //--------------------------------------------------------------------------------------
    UnloadImage(canvas);
    UnloadImage(parrots);

    CloseWindow();                // Close window and OpenGL context
    //--------------------------------------------------------------------------------------

    return 0;
}

[RobLoach]

Minus-ing the destination coordinates from the source rect makes sense, rather than setting them as the inverse. When the source coordinates are 0,0, there isn't a problem since the srcRect would be minus destination anyway. But if your source rectangle is a sprite, like at 128,64, you'll run into issues since the original srcRect values get lost.

Confirming that you'll want to -= it instead. I've done a similar thing in a small software-rendering system I've been working on here: https://github.com/RobLoach/pntr/blob/master/pntr.h#L2353-L2360

Pushed up a PR: #3306 .... @mattj1 also recorded a short video demo of the glitch at https://discord.com/channels/426912293134270465/427518168995725317/1150566991162245170 .