OpenGL, objects disappear at a certain z distance

Question

I'm writing a managed OpenGL library in C++, and I'm having a pretty annoying problem. Whenever I set an objects Z coordinate to -2.0 or lower, the object disappears. And at coordinates 0 through -1.9, it doesn't appear to move away from them camera. I have a world matrix (which is multiplied by the objects position to move it), a view matrix (which is just the identity matrix currently) and a projection matrix, which is setup like this:

• FOV: 45.0f
• Aspect Ratio: 1
• zNear: 0.1f
• zFar: 100.0f

using GLMs glm::perspective method. The order the matrices are multiplied by in the shader is world, view, projection, then position.

I can move the object along the X and Y axis perfectly fine. I have depth testing enabled, using GL_LEQUAL. I can change the actually vertices positions to anything I want, and they move away from the camera or towards it perfectly fine. It just seems to be the world matrix acting up. I'm using glm::mat4 for the world matrix, and glm::vec3 for positions. Whats going on here?

I'm also using OpenGL 3.1, GLSL version 140 (1.4?).

Answer 1

Okay, first off, I want to say that for your Projection's Aspect Ratio, you might want to divide the width by the height. (This will give you your aspect ratio, like 1920/1080 = 16:9 Ratio)

Anyway, where are you getting your model matrix? You're saying you're multiplying the world matrix by your objects position? I wanna say that could be a problem. (Although, this could just be me misunderstanding what you're saying)

All I can say is make sure your objects have their own matrices. That would basically be their World Matrix. Also make sure you multiply your ModelViewProj Matrix with your vertex position in your Vertex Shader.

Answer 2

As it turns out, the order I was multiplying my matrices in the shader was wrong. Originally, I had:

gl_Position = worldMatrix * viewMatrix * projectionMatrix * vec4(in_Position, 1.0);

But it works with:

gl_Position = projectionMatrix * viewMatrix * worldMatrix * vec4(in_Position, 1.0);

I always thought MVP was the order they were supposed to be multiplied in, not PVM. Maybe I'm doing something wrong, but as of now this works.