Say the user taps 4 spots on the iphone, defining an irregular 4 sided polygon (in 2d space). Is there a way to map/fit a (potentially highly distorted) image onto this shape, without using OpenGL?
Something like:
Is my only option to somehow calculate the 3d space that my irregular 4 sided shape sits in (based on where the tapped 2d points sit), create an OpenGL plane in that space, and map my texture to it flatly? Seems like there should be an easier way...
Thanks in advance.
Update: After diving into OpenGL I'm almost there... but I still can't get the texture to distort correctly. The triangulation seems to be messing with the texture mapping:
I can't answer your question completely, but one thing I would say is that you don't need to think about any conversion / mapping to 3D. Using OpenGL you can easily draw the shape in 2D and have the texture mapped as you desire. No need for any fancy maths or conversions. It's no more complicated than drawing a rectangle. OpenGL doesn't care that your 4-sided shape isn't actually rectangular.
Related
I managed to create a map divided in chunks. Each one holding a mesh generated by using perlin noise and so on. The basic procedural map method, shown in multiple tutorials.
At this point i took a look at surface shader and managed to write one which fades multiple textures depending on the vertex heights.
This gives me a map which is colored smoothly.
In tutorials i watched they seem to use different methods to texture a mesh. So in this one for example a texture is generated for each mesh. This texture will hold a different color depending on the noise value.This texture is applied to the mesh and after that the mesh vertices are displaced depending on the z-value.
This results in a map with sharper borders between the colors giving the whole thing a different look. I believe there is a way to create smoother transitions between the tile-colors by fading them like i do in my shader.
My question is simply what are the pro and cons of those methods. Let's call them "shader" and "texture map". I am lost right now, not knowing in which direction to go.
I am beating my head a little bit here for a while but I still could bot find a way to set up a matrix that projects my Unity game in a Tibianeske like manner:
Reading on tutorials on internet I could figure out how a normal orthographic perspective works, but tibia's one is kind of odd.
Digging over webs I found in here a guy (Clint Bellanger) who describes really well how to get the same perspective in blender's render according to him:
Start with a scene in 45 degree isometric. Video game style, where
the camera angle is Blender (60,0,45).
In Blender if you look at Buttons Window -> Scene -> Render Buttons ->
Format, you can set the render aspect ratio. Set AspY to half of
AspX. This is the same as taking regular rendered output and scaling
X by 50%. If you rendered a cube, the top of the cube will be a
perfect square (though at a 45 degree angle).
We can then use Blender nodes to rotate the result 45 degrees. The
output:
Note this started as a cube, so there's a lot of "vertical"
distortion. So you might have to scale meshes to 50% Z before using
this method. Also notice the Edge seems to be applied after the
Aspect, so the edge isn't distorted.
Blend file: http://clintbellanger.net/images/temp/UltimaVII.blend (I'm
a Nodes noob so there might be a smarter setup).
For kicks, here is that tower again. I pulled it into the above
workflow scene and scaled Z by 50%. Click "Re-render this layer" on
the first node to create the composite.
On his method, he used stuff like rescaling the render and changing the scale of models, Im convinced I could get along just with the 4x4matrix in unity(or in any other 3d environment really).
Hope someone more experienced with perks of 3D maths could help me to figure it out. Thank you! =D
What you ask for is a simple parallel projection. The typical orthographic projection is just a special case where the projection rays are perpendicular to the image plane. However, every parallel projection can be represented by an affine shear transformation followed by a standard orthogonal projection.
Im convinced I could get along just with the 4x4matrix in unity(or in any other 3d environment really).
Yes. Using default GL conventions here, all you have to do is to take the standard ortho matrix, post-multiply it by an appropriate shear matrix and use that as the projection matrix.
I have a projector component and I need to find the angle that projected texture falls at to exclude the projecting on vertical faces.
My projector is under the mouse pointer and works ok when it is over an horizontal face:
I would like the projector to switch off on vertical faces to avoid this bad effect:
If possible, I would like to do it in the shader code to avoid the vertical projected image even if the cursor is located on the corners of an horizontal face and a part "goes out" on vertical face.
I found this solution in C#:
if (Physics.Raycast(MouseRay,out hitInfo)){
if(hitInfo.normal.y>0) {
// draw
} else {
// not draw
}
}
But only it works on curved surfaces and not, for example, on the face cubes.
How can I do this properly?
Normally they would use an image on a quad using TGA transparency, which rotates itself to the face that the middle of the object is aligned to, using ray to find the vertex and making it's absolute normal.
Other ways of doing it would be quite tricky, perhaps using decals... If you did it using a shader, it would take so much time... it's a case of problem solving not being ordered in order of importance for fast development. Technically you can project a volumetric texture on top of whatever object you are using... that way you can add your barred circle projected from a point in space towards the object, as a mathematical formula, it takes a while to do, check out volumetric textures, i have written some and in your case it needs the mouse pos sent to texture and maths to add transparent zone and red zone to texture. takes all day.
It's fine to have a flat circle that flips around when you change the pointer onto a different face, it will just look like a physical card and it's much easier to code, 10 minutes instead of many hours.
As I understand it, the standard projection model places an imaginary grid in front of the camera, and for each triangle in the scene, determines which 3 pixels its 3 corners project onto. The color is determined for each of these points, and the fragment shader fills in the rest using interpolation.
My question is this: is it possible to gain control over this projection model? For example, create my own custom distorted uv-grid? Or even just supply my own algorithm:
xyPixelPos_for_Vector3( Vector3 v ) {...}
I'm working in Unity3D, so I think that limits me to cG or openGL.
I did once write a GLES2 shader, but I don't remember ever performing any kind of "ray hits quad" type test to resolve the pixel position of a particular 3D point in space.
I'm going to assume that you want to render 3d images based upon 3d primitives that are defined by vertices. This is not the only way to render images with OpenGL but it is the most common. The technique that you describe sounds much more like Ray-Tracing.
How OpenGL Typically Works:
I wouldn't say that OpenGL creates an imaginary grid. Instead, what it does is take the positions of each of your vertices, and converts them into a different space using linear algebra (Matrices).
If you want to start playing around with this, it would be best to do some reading on Matrices, to understand what the graphics card is doing.
You can easily start warping the positions of Vertices by making a vertex shader. However, there is some setup involved. See the Lighthouse tutorials (http://www.lighthouse3d.com/tutorials/glsl-tutorial/hello-world-in-glsl/) to get started with that! You will also want to read their tutorials on lighting (http://www.lighthouse3d.com/tutorials/glsl-tutorial/lighting/), to create a fully functioning vertex shader which includes a lighting model.
Thankfully, once the shader is set up, you can distort your entire scene to your hearts content. Just remember to do your distortions in the right 'space'. World coordinates are much different than eye coordinates!
I'm rendering particles in a 2D game. Each particle is a quad (2 triangles). How can I make the drawing the fastest possible? All the particles has the same texture, I'm only changing it's positions.
Now I'm using a call to glVertexPointer and glDrawArrays for each particle. So I'm sending 4 vertices each time to the GPU.
Is there any other approach that could be faster?
I'm using OpenGL ES 1.1 (iPhone)
Thanks!
Every draw call you make (glDrawArrays) is expensive. Doing this once per particle is DEFINITELY way too often. All your particles can be drawn with a single draw call; just set up a big array of all the triangle verts and another big array with the texture coords, and call glVertexPointer/glDrawArrays once-- that's the power of glVertexPointer: arbitrary geometry of the same type in one call. :)
For what you're doing, you should also look into point sprites (GL_POINTS), which also function as tiny textured quads. They're 2D only, so you can't map your texture into the Z axis, but if your particles are just 2D quads of the same texture over and over, point sprites will likely do exactly what you want.
There's a way to do that all in one draw routine. I THINK it's by adding an extra vertex after each quad, which is the same as the previous vertex, but I could be wrong.
EDIT: After looking into it a bit, it looks like you need two in between; essentially one after, and one before. It does add up to quite a few extra vertexes, but I know from experience that it makes a HUGE positive difference on the iPhone to do it all in one draw operation (we were drawing text from a texture, so essentially the same thing).
EDIT2: Also note, I'm referring to using GL_TRIANGLE_STRIP - if you were using GL_TRIANGLES instead, you wouldn't need the extra vertices... except, then you'd be doing the same amount extra anyway, due to repeating 2 for each second triangle.