64 lines
2.2 KiB
Go
64 lines
2.2 KiB
Go
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// Ported from GLUT's samples. Original copyright below applies.
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/* Copyright (c) Mark J. Kilgard, 1996. */
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/* This program is freely distributable without licensing fees
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and is provided without guarantee or warrantee expressed or
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implied. This program is -not- in the public domain. */
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/* This program is a response to a question posed by Gil Colgate
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<gcolgate@sirius.com> about how lengthy a program is required using
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OpenGL compared to using Direct3D immediate mode to "draw a
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triangle at screen coordinates 0,0, to 200,200 to 20,200, and I
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want it to be blue at the top vertex, red at the left vertex, and
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green at the right vertex". I'm not sure how long the Direct3D
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program is; Gil has used Direct3D and his guess is "about 3000
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lines of code". */
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package main
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import (
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"gl"
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"glut"
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)
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type GLPainter struct {
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}
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func reshape(w, h int) {
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/* Because Gil specified "screen coordinates" (presumably with an
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upper-left origin), this short bit of code sets up the coordinate
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system to correspond to actual window coodrinates. This code
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wouldn't be required if you chose a (more typical in 3D) abstract
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coordinate system. */
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gl.Viewport(0, 0, w, h) /* Establish viewing area to cover entire window. */
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gl.MatrixMode(gl.PROJECTION) /* Start modifying the projection matrix. */
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gl.LoadIdentity() /* Reset project matrix. */
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gl.Ortho(0, float64(w), 0, float64(h), -1, 1) /* Map abstract coords directly to window coords. */
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gl.Scalef(1, -1, 1) /* Invert Y axis so increasing Y goes down. */
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gl.Translatef(0, float32(-h), 0) /* Shift origin up to upper-left corner. */
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}
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func display() {
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gl.Clear(gl.COLOR_BUFFER_BIT)
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gl.Begin(gl.TRIANGLES)
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gl.Color3f(0.0, 0.0, 1.0) /* blue */
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gl.Vertex2i(0, 0)
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gl.Color3f(0.0, 1.0, 0.0) /* green */
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gl.Vertex2i(200, 200)
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gl.Color3f(1.0, 0.0, 0.0) /* red */
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gl.Vertex2i(20, 200)
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gl.End()
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gl.Flush() /* Single buffered, so needs a flush. */
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}
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func main() {
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glut.Init()
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glut.CreateWindow("single triangle")
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glut.DisplayFunc(display)
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glut.ReshapeFunc(reshape)
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glut.MainLoop()
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}
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