How to NOT map vertices to screen

Graphics and GPU Programming Programming

Started by EvilNando May 20, 2011 06:39 PM

4 comments, last by Brother Bob 12 years, 10 months ago

Author

May 20, 2011 06:39 PM

https://github.com/jckarter/hello-gl-ch3/blob/master/hello-gl.c
According the example Ive been following, this structure is used for creating the vertices:





/*

 * Data used to seed our vertex array and element array buffers:

 */

static const GLfloat g_vertex_buffer_data[] = { 

    -1.0f, -1.0f, 0.0f, 1.0f,

     1.0f, -1.0f, 0.0f, 1.0f,

    -1.0f,  1.0f, 0.0f, 1.0f,

     1.0f,  1.0f, 0.0f, 1.0f

};

static const GLushort g_element_buffer_data[] = { 0, 1, 2, 3 };

where do these vertices get assigned to screen space, I would like to get an actual quad of 1pixel instead to whatever my current gl_surface is

dpadam450

2,403

May 23, 2011 10:32 PM

map -1 to 1, to 0 to window width/height

-1 becomes 0, 1 becomes window width

width, height = 640 x 480
-1.0*(640/2.0) = -320 , -320 + (640/2.0) = 0 , -1 became 0
1*(640/2.0) = 320, 320 + (640/2.0) = 1, 1 becomes window width

Follow that and your fine. Or if in 2D, u can use glOrtho(0,windowwidht, 0, windowheight); and then your g_vertex_buffer just holds pixel locations instead of -1 to 1 values.

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EvilNando

Author

May 24, 2011 01:47 PM

Any idea of what would be the equivalent of glOrtho in opengl 3.2?

Brother Bob

10,350

May 24, 2011 02:02 PM

The matrix generated by glOrtho can be found in any decent documentation or reference manual. Your favorite linear algebra library should also contain functions to generate orthogonal projection matrices. Just multiply your vertices by that matrix in your vertex program.

EvilNando

Author

May 24, 2011 02:04 PM

The matrix generated by glOrtho can be found in any decent documentation or reference manual. Your favorite linear algebra library should also contain functions to generate orthogonal projection matrices. Just multiply your vertices by that matrix in your vertex program.

Then I have to create the matrix at the shader level? or is there a way to pass a custom data type to the shader as an attribute

sorry Im very noob at this xD

Brother Bob

10,350

May 24, 2011 02:10 PM

You use the glUniform family of functions and a uniform variable in your shader.

How to NOT map vertices to screen

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How to NOT map vertices to screen

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