Signature of DrawTriangles() - what is img for?

[tomekc]

Hello,

I have trouble understanding the method signature. In my use case, I just want to draw vector lines in the specified color.
What is the purpose of img argument? It is not stated clearly in the comments.

I ended up giving a random image for this argument because even though it is a pointer, the program crashes when it is null.

func (i *Image) DrawTriangles(vertices []Vertex, indices []uint16, img *Image, options *DrawTrianglesOptions)

[hajimehoshi]

Hi,

The given image is used in the same manner as DrawImage. The image is rendered on the triangles specified by the given vectors and indices. The texture coordinates are specified by the vertices. See Vertex definition.

[tomekc]

Thanks. So this is intended to draw a textured polygon specified by triangles?

In that case, is there a way to draw primitive shapes, like lines, maybe rectangles?

[hajimehoshi]

Good question. I'd use a white empty image. See https://github.com/hajimehoshi/ebiten/blob/master/examples/polygons/main.go

[tomekc]

Thanks, a bit hacky, but still a solution :)

In the example, I see that you created an empty 3x3 image, and during the drawing, a routine used sub-image 1,1 - 2,2. I guess that was necessary?

[hajimehoshi]

Thanks, a bit hacky, but still a solution :)

I admit this seems hacky but I chose the ease of expecting the API behavior.

Another suggestion is to use DrawTrianglesWithShader with your custom shader, but I think this is overkill.

In the example, I see that you created an empty 3x3 image, and during the drawing, a routine used sub-image 1,1 - 2,2. I guess that was necessary?

Yes. Otherwise, the edges would be missing.