How to convert screen to world coordinates in OpenGL?
And the window I created for an opengl program is 640 pixles in width and 480 pixels in height. The top left pixel is (0,0), the button right pixel is (640, 480) I also wrote a function to retrive the coordinates when I click and drag and release the mouse button (When I click, it’s (x1,y1) and when I release it’s (x2,y2) )
How are the coordinates of the screen determined?
The division needs to be by the number of pixels in each coordinate direction, because you do have 640/480 pixels within the coordinate range. One subtle detail to take into account is that, when you get a given position from your mouse input, these will be the integer coordinates of the pixels.
How many pixels are in each coordinate range?
The answer given by @BDL might get you close enough for what you need, but the calculations are not really correct. The division needs to be by the number of pixels in each coordinate direction, because you do have 640/480 pixels within the coordinate range.
How big is the clipping area in OpenGL?
So the default 2d clipping area of opengl is left -1.0 to right 1.0, and buttom -1.0 to top 1.0 And the window I created for an opengl program is 640 pixles in width and 480 pixels in height. The top left pixel is (0,0), the button right pixel is (640, 480)
Which is the center of the pixel in OpenGL?
But what you most likely want is the center of the pixel. To precisely transform this into the OpenGL coordinate space, you can simply apply a 0.5 offset to your input value, moving the value from the edge to the center of the pixel. For example, the left most pixel would have x-coordinate 0, the right most 639.
How to write a simple Shader in OpenGL?
Simple Shader 1. This shader is the simplest shader that we are able to write; that is, a mesh will be drawn with a plain color and we will play with the vertex shader parameters. First, create an empty project called “simple1.” This action will create the .gdp file containing all OpenGL states that the shader needs.
When do you apply perspective division in OpenGL?
OpenGL requires that the visible coordinates fall between the range -1.0 and 1.0 as the final vertex shader output, thus once the coordinates are in clip space, perspective division is applied to the clip space coordinates: o u t = (x / w y / w z / w)
What happens at the end of a vertex shader in OpenGL?
At the end of each vertex shader run, OpenGL expects the coordinates to be within a specific range and any coordinate that falls outside this range is clipped. Coordinates that are clipped are discarded, so the remaining coordinates will end up as fragments visible on your screen.
How to calculate inverse matrix for screen coordinates?
See the answers to the Stack Overflow Question inverting a 4×4 matrix to see how to calculate a inverse matrix: To map a point from viewport (screen) coordinates to the NDC you have to map the X-coordinate and the Y-coordinate to the range (-1.0, 1.0).