![]() ![]() For one thing, objects that are farther away from the viewer in 3D look smaller in the 2D image. (The illusion is much stronger if you can rotate the image.) Several things contribute to the effect. This example is a 2D image, but it has a 3D look. The on-line version of this section has a demo version of this image in which you drag on the axes to rotate the image. The x-axis is green, the y-axis is blue, and the z-axis is red. The positive directions of the x, y, and z axes are shown as big arrows. This image illustrates a 3D coordinate system. ![]() The z-axis is perpendicular to both the x-axis and the y-axis. (That’s essentially what it means to be three dimensional.) The third coordinate is often called z. In three dimensions, you need three numbers to specify a point. We have seen the power of this when we discussed transforms, which are defined mathematically in terms of coordinates but which have real, useful physical meanings. Points and objects are real things, but coordinates are just numbers that we assign to them so that we can refer to them easily and work with them mathematically. More than that, the assignment of pairs of numbers to points is itself arbitrary to a large extent. The coordinates are often referred to as x and y, although of course, the names are arbitrary. In two dimensions, you need a pair of numbers to specify a point. GlRotatef(57.\)Ī coordinate system is a way of assigning numbers to points. Since I need to do these modifications rather quickly, I’ve just created a function that take as input an array of vertices and get the ModelView projection matrix and apply it to my vertices (before I create the VBO.) glPushMatrix() I am indeed trying to change my code in order to avoid use of glTransformation… In fact, the matrix stacks are deprecated in GL 3.0 for precisely this reason - fixed function is gone and in shaders, the built-in matrices don’t necessarily have a defined meaning.Cheers, That way, you can have as many matrices and coordinate spaces as you need. Roll your own matrix class and pass the matrices to the shader as uniforms. This is kind of hacky, but as this is all shader code and you can use the matrices for whatever you want, you should be good to go. Use the model-view matrix as just a model matrix, use a texture matrix as your view matrix. Abuse one of the other matrix stacks (such as the texture matrices). It would also break some other stuff like gl_NormalMatrix. Of course, then you’d lose your eye coordinates (which are often needed for lighting). Then, your world coordinates will simply be: gl_ModelViewMatrix * gl_Vertex ![]() calls that take your vertices from world space to eye space on your projection matrix, and only use the model-view matrix for object to world coordinate transformation. That means, do all your glTranslatef, glRotatef, etc. ![]() Essentially, you’re creating a gl_Model matrix and a gl_ViewProjection matrix. Use the model-view matrix stack as a model matrix and use bake your world-eye coordinate transformation into the projection matrix. The good news is that, because you’re using shaders, the matrix stacks don’t necessarily have to be used for the purposes they are named for. However, in OpenGL, the model matrix and view matrix are implicitly concatenated (hence, the term modelview matrix) and therefore, you don’t really have access to world coordinates. The issue you’re having is that there are actually four coordinate spaces (object, world, view, clip) and only two matrix stacks. ![]()
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