[solved] How to get Texture from Quad

[Xii]

I have a shader, and when I create a new Image and a new Quad from that Image, then try to pass the Quad to the shader it errors with: "bad argument #3 to 'gl_send' (Texture expected, got Quad)".

How do I get the Texture from the Quad?

The wiki says nothing on Textures.

I'm trying to render a part from a sprite atlas with a shader.

[pgimeno]

A quad is mostly an object holding four coordinates and the width/height of a texture, but not the texture itself; you can use the same quad for different textures.

You can't send a quad to a shader. You can send the texture, and use Quad:getTextureDimensions and Quad:getViewport to send them to the shader and draw the correct texture fragment with some math.

[Xii]

So what you're saying is, I need to edit the shader to draw only part of the texture?

[pgimeno]

Yes, basically.

[ReFreezed]

To render a part of a texture you give love.graphics.draw both the texture and the quad. No shaders are required to do that. If you only give love.graphics.draw a texture then LÖVE automatically uses a quad that spans the whole texture.

[Xii]

Thank you for your assistance pgimeno, the shader now draws the specified part.

To render a part of a texture you give love.graphics.draw both the texture and the quad. No shaders are required to do that. If you only give love.graphics.draw a texture then LÖVE automatically uses a quad that spans the whole texture.

The shader I have is a requirement. Not optional. Anyhow, the original issue is resolved.

[zorg]

Thank you for your assistance pgimeno, the shader now draws the specified part.

To render a part of a texture you give love.graphics.draw both the texture and the quad. No shaders are required to do that. If you only give love.graphics.draw a texture then LÖVE automatically uses a quad that spans the whole texture.

The shader I have is a requirement. Not optional. Anyhow, the original issue is resolved.

Without explaining why, i can't really suggest otherwise, but this technically could work:

Code: Select all

function love.draw()
  love.graphics.setShader(yourShader)
  love.graphics.draw(yourImage, yourQuad, 0, 0)
end

[Xii]

Without explaining why,

LÖVE's API to draw quads is awful. Shearing factors? What even is that? I have a custom solution of the form:

draw_textured_quad(texture, tx,ty,tw,th, x1,y1, x2,y2, x3,y3, x4,y4)

Which is much more convenient, as it allows arbitrary quad shapes by specifying the vertices' positions.

[slime]

LÖVE's API to draw quads is awful. Shearing factors? What even is that? I have a custom solution of the form:

draw_textured_quad(texture, tx,ty,tw,th, x1,y1, x2,y2, x3,y3, x4,y4)

Which is much more convenient, as it allows arbitrary quad shapes by specifying the vertices' positions.

This is shear. It's a niche feature, which is why the parameters for it are at the very end of the list in draw(): https://en.wikipedia.org/wiki/Shear_mapping

You can use a mesh if you want arbitrary shapes - you don't need a shader at all. However, with a shader or a mesh people will probably be confused when they expect perspective-correct texture mapping but get an affine mapping instead, since they didn't actually use real 3D coordinates. Meshes can do perspective-correct texture mapping as well, if you give it the right information and have a perspective projection matrix.

[Xii]

You can use a mesh if you want arbitrary shapes [...] Meshes can do perspective-correct texture mapping as well, if you give it the right information and have a perspective projection matrix.

What is the right information?