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/**
* Test variable array indexing in a vertex shader.
* Brian Paul
* 17 April 2009
*/
#include <assert.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <GL/gl.h>
#include <GL/glut.h>
#include <GL/glext.h>
#include "extfuncs.h"
#include "shaderutil.h"
/**
* The vertex position.z is used as a (variable) index into an
* array which returns a new Z value.
*/
static const char *VertShaderText =
"uniform sampler2D tex1; \n"
"uniform float HeightArray[20]; \n"
"void main() \n"
"{ \n"
" vec4 pos = gl_Vertex; \n"
" int i = int(pos.z * 9.5); \n"
" pos.z = HeightArray[i]; \n"
" gl_Position = gl_ModelViewProjectionMatrix * pos; \n"
" gl_FrontColor = pos; \n"
"} \n";
static const char *FragShaderText =
"void main() \n"
"{ \n"
" gl_FragColor = gl_Color; \n"
"} \n";
static GLuint fragShader;
static GLuint vertShader;
static GLuint program;
static GLint win = 0;
static GLboolean Anim = GL_TRUE;
static GLboolean WireFrame = GL_TRUE;
static GLfloat xRot = -70.0f, yRot = 0.0f, zRot = 0.0f;
static void
Idle(void)
{
zRot = 90 + glutGet(GLUT_ELAPSED_TIME) * 0.05;
glutPostRedisplay();
}
/** z=f(x,y) */
static float
fz(float x, float y)
{
return fabs(cos(1.5*x) + cos(1.5*y));
}
static void
DrawMesh(void)
{
GLfloat xmin = -2.0, xmax = 2.0;
GLfloat ymin = -2.0, ymax = 2.0;
GLuint xdivs = 20, ydivs = 20;
GLfloat dx = (xmax - xmin) / xdivs;
GLfloat dy = (ymax - ymin) / ydivs;
GLfloat ds = 1.0 / xdivs, dt = 1.0 / ydivs;
GLfloat x, y, s, t;
GLuint i, j;
y = ymin;
t = 0.0;
for (i = 0; i < ydivs; i++) {
x = xmin;
s = 0.0;
glBegin(GL_QUAD_STRIP);
for (j = 0; j < xdivs; j++) {
float z0 = fz(x, y), z1 = fz(x, y + dy);
glTexCoord2f(s, t);
glVertex3f(x, y, z0);
glTexCoord2f(s, t + dt);
glVertex3f(x, y + dy, z1);
x += dx;
s += ds;
}
glEnd();
y += dy;
t += dt;
}
}
static void
Redisplay(void)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
if (WireFrame)
glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
else
glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
glPushMatrix();
glRotatef(xRot, 1.0f, 0.0f, 0.0f);
glRotatef(yRot, 0.0f, 1.0f, 0.0f);
glRotatef(zRot, 0.0f, 0.0f, 1.0f);
glPushMatrix();
DrawMesh();
glPopMatrix();
glPopMatrix();
glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
glutSwapBuffers();
}
static void
Reshape(int width, int height)
{
glViewport(0, 0, width, height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glFrustum(-1.0, 1.0, -1.0, 1.0, 5.0, 25.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0.0f, 0.0f, -15.0f);
}
static void
CleanUp(void)
{
glDeleteShader_func(fragShader);
glDeleteShader_func(vertShader);
glDeleteProgram_func(program);
glutDestroyWindow(win);
}
static void
Key(unsigned char key, int x, int y)
{
const GLfloat step = 2.0;
(void) x;
(void) y;
switch(key) {
case 'a':
Anim = !Anim;
if (Anim)
glutIdleFunc(Idle);
else
glutIdleFunc(NULL);
break;
case 'w':
WireFrame = !WireFrame;
break;
case 'z':
zRot += step;
break;
case 'Z':
zRot -= step;
break;
case 27:
CleanUp();
exit(0);
break;
}
glutPostRedisplay();
}
static void
SpecialKey(int key, int x, int y)
{
const GLfloat step = 2.0;
(void) x;
(void) y;
switch(key) {
case GLUT_KEY_UP:
xRot += step;
break;
case GLUT_KEY_DOWN:
xRot -= step;
break;
case GLUT_KEY_LEFT:
yRot -= step;
break;
case GLUT_KEY_RIGHT:
yRot += step;
break;
}
glutPostRedisplay();
}
static void
Init(void)
{
GLfloat HeightArray[20];
GLint u, i;
if (!ShadersSupported())
exit(1);
GetExtensionFuncs();
vertShader = CompileShaderText(GL_VERTEX_SHADER, VertShaderText);
fragShader = CompileShaderText(GL_FRAGMENT_SHADER, FragShaderText);
program = LinkShaders(vertShader, fragShader);
glUseProgram_func(program);
/* Setup the HeightArray[] uniform */
for (i = 0; i < 20; i++)
HeightArray[i] = i / 20.0;
u = glGetUniformLocation_func(program, "HeightArray");
glUniform1fv_func(u, 20, HeightArray);
assert(glGetError() == 0);
glClearColor(0.4f, 0.4f, 0.8f, 0.0f);
glEnable(GL_DEPTH_TEST);
glColor3f(1, 1, 1);
}
int
main(int argc, char *argv[])
{
glutInit(&argc, argv);
glutInitWindowSize(500, 500);
glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
win = glutCreateWindow(argv[0]);
glutReshapeFunc(Reshape);
glutKeyboardFunc(Key);
glutSpecialFunc(SpecialKey);
glutDisplayFunc(Redisplay);
Init();
if (Anim)
glutIdleFunc(Idle);
glutMainLoop();
return 0;
}
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