1 //
2 // Book: OpenGL(R) ES 2.0 Programming Guide
3 // Authors: Aaftab Munshi, Dan Ginsburg, Dave Shreiner
4 // ISBN-10: 0321502795
5 // ISBN-13: 9780321502797
6 // Publisher: Addison-Wesley Professional
7 // URLs: http://safari.informit.com/9780321563835
8 // http://www.opengles-book.com
9 //
10
11 // Simple_VertexShader.c
12 //
13 // This is a simple example that draws a rotating cube in perspective
14 // using a vertex shader to transform the object
15 //
16 #include <stdlib.h>
17 #include "esUtil.h"
18
19 typedef struct
20 {
21 // Handle to a program object
22 GLuint programObject;
23
24 // Attribute locations
25 GLint positionLoc;
26
27 // Uniform locations
28 GLint mvpLoc;
29
30 // Vertex daata
31 GLfloat *vertices;
32 GLushort *indices;
33 int numIndices;
34
35 // Rotation angle
36 GLfloat angle;
37
38 // MVP matrix
39 ESMatrix mvpMatrix;
40 } UserData;
41
42 ///
43 // Initialize the shader and program object
44 //
Init(ESContext * esContext)45 int Init ( ESContext *esContext )
46 {
47 UserData *userData = esContext->userData;
48 GLbyte vShaderStr[] =
49 "uniform mat4 u_mvpMatrix; \n"
50 "attribute vec4 a_position; \n"
51 "void main() \n"
52 "{ \n"
53 " gl_Position = u_mvpMatrix * a_position; \n"
54 "} \n";
55
56 GLbyte fShaderStr[] =
57 "precision mediump float; \n"
58 "void main() \n"
59 "{ \n"
60 " gl_FragColor = vec4( 1.0, 0.0, 0.0, 1.0 ); \n"
61 "} \n";
62
63 // Load the shaders and get a linked program object
64 userData->programObject = esLoadProgram ( vShaderStr, fShaderStr );
65
66 // Get the attribute locations
67 userData->positionLoc = glGetAttribLocation ( userData->programObject, "a_position" );
68
69 // Get the uniform locations
70 userData->mvpLoc = glGetUniformLocation( userData->programObject, "u_mvpMatrix" );
71
72 // Generate the vertex data
73 userData->numIndices = esGenCube( 1.0, &userData->vertices,
74 NULL, NULL, &userData->indices );
75
76 // Starting rotation angle for the cube
77 userData->angle = 45.0f;
78
79 glClearColor ( 0.0f, 0.0f, 0.0f, 0.0f );
80 return TRUE;
81 }
82
83
84 ///
85 // Update MVP matrix based on time
86 //
Update(ESContext * esContext,float deltaTime)87 void Update ( ESContext *esContext, float deltaTime )
88 {
89 UserData *userData = (UserData*) esContext->userData;
90 ESMatrix perspective;
91 ESMatrix modelview;
92 float aspect;
93
94 // Compute a rotation angle based on time to rotate the cube
95 userData->angle += ( deltaTime * 40.0f );
96 if( userData->angle >= 360.0f )
97 userData->angle -= 360.0f;
98
99 // Compute the window aspect ratio
100 aspect = (GLfloat) esContext->width / (GLfloat) esContext->height;
101
102 // Generate a perspective matrix with a 60 degree FOV
103 esMatrixLoadIdentity( &perspective );
104 esPerspective( &perspective, 60.0f, aspect, 1.0f, 20.0f );
105
106 // Generate a model view matrix to rotate/translate the cube
107 esMatrixLoadIdentity( &modelview );
108
109 // Translate away from the viewer
110 esTranslate( &modelview, 0.0, 0.0, -2.0 );
111
112 // Rotate the cube
113 esRotate( &modelview, userData->angle, 1.0, 0.0, 1.0 );
114
115 // Compute the final MVP by multiplying the
116 // modevleiw and perspective matrices together
117 esMatrixMultiply( &userData->mvpMatrix, &modelview, &perspective );
118 }
119
120 ///
121 // Draw a triangle using the shader pair created in Init()
122 //
Draw(ESContext * esContext)123 void Draw ( ESContext *esContext )
124 {
125 UserData *userData = esContext->userData;
126
127 // Set the viewport
128 glViewport ( 0, 0, esContext->width, esContext->height );
129
130
131 // Clear the color buffer
132 glClear ( GL_COLOR_BUFFER_BIT );
133
134 // Use the program object
135 glUseProgram ( userData->programObject );
136
137 // Load the vertex position
138 glVertexAttribPointer ( userData->positionLoc, 3, GL_FLOAT,
139 GL_FALSE, 3 * sizeof(GLfloat), userData->vertices );
140
141 glEnableVertexAttribArray ( userData->positionLoc );
142
143
144 // Load the MVP matrix
145 glUniformMatrix4fv( userData->mvpLoc, 1, GL_FALSE, (GLfloat*) &userData->mvpMatrix.m[0][0] );
146
147 // Draw the cube
148 glDrawElements ( GL_TRIANGLES, userData->numIndices, GL_UNSIGNED_SHORT, userData->indices );
149
150 eglSwapBuffers ( esContext->eglDisplay, esContext->eglSurface );
151 }
152
153 ///
154 // Cleanup
155 //
ShutDown(ESContext * esContext)156 void ShutDown ( ESContext *esContext )
157 {
158 UserData *userData = esContext->userData;
159
160 if ( userData->vertices != NULL )
161 {
162 free ( userData->vertices );
163 }
164
165 if ( userData->indices != NULL )
166 {
167 free ( userData->indices );
168 }
169
170 // Delete program object
171 glDeleteProgram ( userData->programObject );
172 }
173
174
main(int argc,char * argv[])175 int main ( int argc, char *argv[] )
176 {
177 ESContext esContext;
178 UserData userData;
179
180 esInitContext ( &esContext );
181 esContext.userData = &userData;
182
183 esCreateWindow ( &esContext, TEXT("Simple Vertex Shader"), 320, 240, ES_WINDOW_RGB );
184
185 if ( !Init ( &esContext ) )
186 return 0;
187
188 esRegisterDrawFunc ( &esContext, Draw );
189 esRegisterUpdateFunc ( &esContext, Update );
190
191 esMainLoop ( &esContext );
192
193 ShutDown ( &esContext );
194 }
195