initial commit

3 files changed, 790 insertions, 0 deletions

diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..3774e47
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,25 @@
+PROG = shader
+OBJS = $(PROG).o
+CC = gcc
+DBGFLAGS = -g -O0
+ifdef DEBUG
+    CFLAGS = $(DBGFLAGS) -Wall -std=c99
+else
+    CFLAGS = -Wall -std=c99 -O2 -march=native -mtune=native
+endif
+LDFLAGS = -lGLEW -lGL -lGLU -lm -lglut
+SDL_CFLAGS := $(shell sdl-config --cflags)
+SDL_LDFLAGS := $(shell sdl-config --libs)
+SDL_image_CFLAGS := $(shell pkg-config --cflags SDL_image)
+SDL_image_LDFLAGS := $(shell pkg-config --libs SDL_image)
+
+$(PROG): $(OBJS)
+	$(CC) $(LDFLAGS) $(SDL_LDFLAGS) $(SDL_image_LDFLAGS) $(OBJS) -o $(PROG)
+
+$(PROG).o: $(PROG).c
+	$(CC) -c $(CFLAGS) $(SDL_CFLAGS) $(SDL_image_CFLAGS) $(PROG).c
+
+.PHONY: clean
+
+clean:
+	rm -f *.o ./$(PROG)
diff --git a/mingw32 b/mingw32
new file mode 100644
index 0000000..0f6649f
--- /dev/null
+++ b/mingw32
@@ -0,0 +1,45 @@
+BIN = shader
+SRC = shader.c
+CC = gcc
+CFLAGS = -Wall -std=c99 -MD
+DBGFLAGS = -g -O0
+ifdef DEBUG
+    CFLAGS += $(DBGFLAGS)
+else
+    CFLAGS += -O2 -march=native -mtune=native
+endif
+LDFLAGS = -lglew32 -lopengl32 -lglu32 -lm -lfreeglut -lmingw32 -lsdlmain -lsdl \
+          -lsdl_image -mwindows
+
+OBJ_DIR = obj
+DEPS_DIR = obj
+BIN_DIR = .
+
+C_FILES = $(filter %.c, $(SRC))
+DEP_FILES = $(addprefix $(DEPS_DIR)\, $(addsuffix .d, $(notdir $(subst .c,,$(SRC)))))
+OBJ_FILES = $(addprefix $(OBJ_DIR)\, $(addsuffix .o, $(notdir $(subst .c,,$(SRC)))))
+
+INCL = -I/include
+
+define C_template
+$(1): $(2)
+	@mkdir -p $$(OBJ_DIR)
+	@mkdir -p $$(DEPS_DIR)
+	$$(CC) -c $$(CFLAGS) $$(INCL) $$< -o $$@
+endef
+
+all: $(BIN)
+
+$(foreach cfile, $(C_FILES), $(eval $(call C_template, $(OBJ_DIR)\$(notdir $(subst .c,,$(cfile))).o, $(cfile))))
+
+$(BIN): $(OBJ_FILES)
+	@mkdir -p $(BIN_DIR)
+	$(CC) -o $(BIN_DIR)/$@ $(OBJ_FILES) $(LDFLAGS)
+
+.PHONY: clean
+
+clean:
+	rm -rf $(OBJ_DIR)
+	rm -f $(BIN_DIR)/$(BIN).exe stdout.txt stderr.txt
+
+-include $(DEP_FILES)
diff --git a/shader.c b/shader.c
new file mode 100644
index 0000000..60b9a11
--- /dev/null
+++ b/shader.c
@@ -0,0 +1,720 @@
+/* shader.c
+ *
+ * Kamil Kaminski
+ * kkaminsk.com
+ *
+ * Example of using a VBO with programmable pipeline on OpenGL 2.1
+ *
+ *
+ */
+
+#include <SDL/SDL.h>
+#include <SDL/SDL_image.h>
+#include <GL/glew.h>
+#include <GL/freeglut.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <math.h>
+
+#define  BUFFER_OFFSET(i) ((char *)NULL + (i))
+
+/* for simplicity we pack */
+/* this structure represents a point with attributes */
+#pragma pack(1)
+typedef struct gltpoint
+{
+    GLfloat normal[3];
+    GLfloat texcoord[2];
+    GLubyte color[3];
+} gltpoint_t;
+#pragma pack()
+
+/* globals */
+int program_running = 1;
+SDL_Surface *screen;
+GLuint buffer_objects[3];
+
+const GLchar vshader[] =
+    "void main(void)\n"
+    "{\n"
+    "    // normal MVP transform\n"
+    "    vec4 clipCoord = gl_ModelViewProjectionMatrix * gl_Vertex;\n"
+    "    gl_Position = clipCoord;\n"
+    "\n"
+    "    // Copy the primary color\n"
+    "    gl_FrontColor = gl_Color;\n"
+    "\n"
+    "    // Calculate NDC\n"
+    "    vec4 ndc = vec4(clipCoord.xyz, 0) / clipCoord.w;\n"
+    "\n"
+    "    // Map from [-1,1] to [0,1] before outputting\n"
+    "    gl_FrontSecondaryColor = (ndc * 0.5) + 0.5;\n"
+    "}\n";
+
+const GLchar fshader[] =
+    "uniform float flickerFactor;\n"
+    "\n"
+    "void main(void)\n"
+    "{\n"
+    "    // Mix primary and secondary colors, 50/50\n"
+    "    vec4 temp = mix(gl_Color, vec4(vec3(gl_SecondaryColor), 1.0), 0.5);\n"
+    "\n"
+    "    // Multiply by flicker factor\n"
+    "    gl_FragColor = temp * flickerFactor;\n"
+    "}\n";
+
+/* few light arrays */
+const GLfloat fNoLight[]     = { 0.0f, 0.0f, 0.0f, 1.0f    };
+const GLfloat fLowLight[]    = { 0.25f, 0.25f, 0.25f, 1.0f };
+const GLfloat fMedLight[]    = { 0.50f, 0.50f, 0.50f, 1.0f };
+const GLfloat fShinyLight[]  = { 0.70f, 0.70f, 0.70f, 1.0f };
+const GLfloat fBrightLight[] = { 1.0f, 1.0f, 1.0f, 1.0f    };
+
+/* light values and coordinates */
+const GLfloat lightPos[]     = { -10.f, 5.0f, 5.0f, 1.0f   };
+
+struct
+{
+    GLuint prog, vert, frag;
+} p;
+
+/* function prototypes */
+static size_t loadfile_to_mem(char *, char **);
+static int vertprog_create(GLuint *, const char *);
+static int fragprog_create(GLuint *, const char *);
+static int prog_create(GLuint *, GLuint *, GLuint *);
+static int gltGenVBOInterleaved(GLuint *, float *, float *, float *,
+           unsigned char *, unsigned short *, GLsizeiptr, GLsizeiptr);
+static int gltDrawVBOInterleaved(GLuint *, size_t, GLenum);
+static void gl_error_check(const char *, const char *, const int);
+static void resize(int, int);
+static void keys(SDL_keysym *, unsigned int *);
+static void process_events(void);
+static void render(void);
+static void setup_sdl(void);
+static void setup_glew(void);
+static void setup_opengl(void);
+static void dump_shaders(void);
+
+/* populates param memory with content of the file param fname */
+static size_t loadfile_to_mem(char *fname, char **memory)
+{
+    if (!fname || !memory)
+        return 0;
+
+    size_t bytes = 0;
+    FILE *file = fopen(fname, "rt");
+
+    if (file != NULL)
+    {
+        fseek(file, 0, SEEK_END);
+        size_t end = ftell(file);
+        fseek(file, 0, SEEK_SET);
+       
+        *memory = (char *) malloc(sizeof(char) * end);
+        if (!memory)
+        {
+            fprintf(stderr, "%s failed, %s:%d\n", __FUNCTION__, __FILE__, __LINE__);
+            perror("malloc");
+            fclose(file);
+            return 0;
+        }
+
+        bytes = fread(*memory, sizeof(char), end, file);
+        fclose(file);
+    }
+    else
+    {
+        fprintf(stderr, "%s: failed to open \"%s\", %s:%d\n",
+                __FUNCTION__, fname, __FILE__, __LINE__);
+        perror("fopen");
+    }
+
+    return bytes;
+}
+
+/* we have a separate buffer objects for vertex data, attributes, and indices
+ * interleaved arrays improve cache performance, the key is locality
+ * for simplicity, vertex is composed of 3 components and texcoord of 2 components
+ */
+static int gltGenVBOInterleaved(GLuint *bufferobjects, float *vert_arr,
+           float *texcoord_arr, float *norm_arr, unsigned char *color_arr,
+           unsigned short *indices_arr, GLsizeiptr points_n, GLsizeiptr indices_n)
+{
+    if (!bufferobjects || !vert_arr || !texcoord_arr || !norm_arr || !color_arr ||
+        !indices_arr || !points_n || !indices_n)
+        return -1;
+
+    /* create an interleaved data structure, is it worth the cpu time? */
+    GLsizeiptr attrib_buff_sz = ((points_n * (3+2) * sizeof(GLfloat)) +
+                                 (points_n * 3 * sizeof(GLubyte)));
+
+    if ((attrib_buff_sz % sizeof(gltpoint_t)) != 0)
+    {
+        fprintf(stderr, "%s: fatal, gltpoint_t appears to be padded!\n", __FUNCTION__);
+        return -1;
+    }
+
+    /* I call point a "vbo slice" */
+    size_t slices_n = attrib_buff_sz / sizeof(gltpoint_t);
+
+    gltpoint_t *gltpoints_arr = (gltpoint_t *) malloc(attrib_buff_sz);
+    if (!gltpoints_arr)
+    {
+        fprintf(stderr, "%s failed, %s:%d\n", __FUNCTION__, __FILE__, __LINE__);
+        perror("malloc");
+        return -1;
+    }
+
+    /* build interleaved data structure, seems cache friendly */
+    int i;
+    for (i = 0; i < slices_n; i++)
+    {
+        gltpoints_arr[i].normal[0]   = norm_arr[i * 3 + 0];
+        gltpoints_arr[i].normal[1]   = norm_arr[i * 3 + 1];
+        gltpoints_arr[i].normal[2]   = norm_arr[i * 3 + 2];
+        gltpoints_arr[i].texcoord[0] = texcoord_arr[i * 2 + 0];
+        gltpoints_arr[i].texcoord[1] = texcoord_arr[i * 2 + 1];
+        gltpoints_arr[i].color[0]    = color_arr[i * 3 + 0];
+        gltpoints_arr[i].color[1]    = color_arr[i * 3 + 1];
+        gltpoints_arr[i].color[2]    = color_arr[i * 3 + 2];
+    }
+
+    glGenBuffers(3, bufferobjects);
+
+    /* vertex data */
+    glBindBuffer(GL_ARRAY_BUFFER, bufferobjects[0]);
+    glBufferData(GL_ARRAY_BUFFER, points_n * 3 * sizeof(float),
+                 (const GLvoid *) vert_arr, GL_STATIC_DRAW);
+
+    /* attribute data, normals, texcoords, and color */
+    glBindBuffer(GL_ARRAY_BUFFER, bufferobjects[1]);
+    glBufferData(GL_ARRAY_BUFFER, attrib_buff_sz,
+                 (const GLvoid *) gltpoints_arr, GL_STATIC_DRAW);
+
+    /* indices data */
+    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, bufferobjects[2]);
+    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(unsigned short) * indices_n,
+                 (const GLvoid *) indices_arr, GL_STATIC_DRAW);
+
+    free(gltpoints_arr);
+
+    return 0;
+}
+
+static int gltDrawVBOInterleaved(GLuint *bufferobjects, size_t indices_n, GLenum mode)
+{
+    if (!bufferobjects || !indices_n)
+        return -1;
+
+    glEnableClientState(GL_VERTEX_ARRAY);
+    glEnableClientState(GL_NORMAL_ARRAY);
+    glEnableClientState(GL_TEXTURE_COORD_ARRAY);
+    glEnableClientState(GL_COLOR_ARRAY);
+
+    /* vertex data */
+    glBindBuffer(GL_ARRAY_BUFFER, bufferobjects[0]);
+    glVertexPointer(3, GL_FLOAT, 0, BUFFER_OFFSET(0));
+
+    /* attribute data, normals, texcoords, and color */
+    glBindBuffer(GL_ARRAY_BUFFER, bufferobjects[1]);
+    glNormalPointer(GL_FLOAT, sizeof(gltpoint_t), BUFFER_OFFSET(0));
+    glClientActiveTexture(GL_TEXTURE0);
+    glTexCoordPointer(2, GL_FLOAT, sizeof(gltpoint_t), BUFFER_OFFSET(sizeof(GLfloat) * 3));
+    glColorPointer(3, GL_UNSIGNED_BYTE, sizeof(gltpoint_t), BUFFER_OFFSET(sizeof(GLfloat) * 5));
+
+    /* indices data */
+    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, bufferobjects[2]);
+    glDrawElements(mode, indices_n, GL_UNSIGNED_SHORT, 0);
+
+    glDisableClientState(GL_VERTEX_ARRAY);
+    glDisableClientState(GL_NORMAL_ARRAY);
+    glDisableClientState(GL_TEXTURE_COORD_ARRAY);
+    glDisableClientState(GL_COLOR_ARRAY);
+
+    return 0;
+}
+
+static void gl_error_check(const char *func, const char *file, const int line)
+{
+    GLenum err_code;
+    const GLubyte *err_str;
+
+    /* this single poke pops of the error from opengl state, hence the do loop */
+    if ((err_code = glGetError()) != GL_NO_ERROR)
+    {
+        fprintf(stderr, "errors encountered leading up to: %s in %s:%d\n",
+                func, file, line);
+
+        do
+        {
+            err_str = gluErrorString(err_code);
+            fprintf(stderr, "OpenGL error: %s\n", err_str);
+        }
+        while ((err_code = glGetError()) != GL_NO_ERROR);
+    }
+}
+
+static void resize(int w, int h)
+{
+    printf("window: resizing to %dx%d\n", w, h);
+    GLfloat fAspect = (GLfloat) w / (GLfloat) h;
+    if (h == 0)
+        h = 1;
+    glViewport(0, 0, w, h);
+
+    /* reset coordinate system */
+    glMatrixMode(GL_PROJECTION);
+    glLoadIdentity();
+
+    /* produce the perspective projection */
+    /* void gluPerspective(GLdouble fovy, GLdouble aspect, GLdouble zNear, GLdouble zFar) */
+    gluPerspective(40.0f, fAspect, 1.0, 40.0);
+
+    glMatrixMode(GL_MODELVIEW);
+    glLoadIdentity();
+
+    /* this needs to be ran again, glut does it for you I suppose */
+    SDL_SetVideoMode(w, h, 32, SDL_OPENGL | SDL_RESIZABLE);
+}
+
+static void setup_opengl(void)
+{
+    /* setup fog */
+    glEnable(GL_FOG);
+    glFogfv(GL_FOG_COLOR, fLowLight); /* set fog color to match background */
+    glFogf(GL_FOG_START, 4.0f);
+    glFogf(GL_FOG_END, 20.0f);
+    glFogi(GL_FOG_MODE, GL_LINEAR);   /* fog equation */
+
+    glEnable(GL_DEPTH_TEST); /* hidden surface removal, aka Z-buffer */
+    glFrontFace(GL_CCW);     /* counter clock-wise polygons face out */
+    glEnable(GL_CULL_FACE);  /* do not calculate inside of a pyramid */
+
+    /* enable lighting, primitives now need to define color properties */
+    glEnable(GL_LIGHTING);
+
+    /* global illumination, ambient RGBA intensity of the entire scene */
+    glLightModelfv(GL_LIGHT_MODEL_AMBIENT, fLowLight);
+
+    /* setup and enable light 0 */
+    glLightfv(GL_LIGHT0, GL_AMBIENT,  fMedLight);
+    glLightfv(GL_LIGHT0, GL_DIFFUSE,  fShinyLight);
+    glLightfv(GL_LIGHT0, GL_SPECULAR, fBrightLight);
+    glLightfv(GL_LIGHT0, GL_POSITION, lightPos);
+    glEnable(GL_LIGHT0);
+
+    /* set material properties to follow all glColor values */
+    /* all primitives specified after the glMaterial call are affected by the
+     * last values set, until another call to glMaterial is made */
+    glColorMaterial(GL_FRONT, GL_AMBIENT_AND_DIFFUSE);
+
+    /* enable color tracking, should be called after glColorMaterial */
+    glEnable(GL_COLOR_MATERIAL);
+
+    /* set globally, sets specular reflection to a white color,
+     * this call follows all subsequent primitives */
+    glMaterialfv(GL_FRONT, GL_SPECULAR, fBrightLight);
+
+    /* default (0), by increasing this value you reduce the size and increase
+     * the focus of the specular highlight, causing a shiny spot to appear */
+    glMateriali(GL_FRONT, GL_SHININESS, 64);
+
+    /* multisampling for polygons, conflicts with *polygon* anti-aliasing */
+    /* enabled by default, that's what man page says, hmmm! */
+    glEnable(GL_MULTISAMPLE);
+
+    /* AA is disabled, but we will keep the blending function and hints though */
+    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
+    glHint(GL_POINT_SMOOTH_HINT, GL_NICEST);
+    glHint(GL_LINE_SMOOTH_HINT, GL_NICEST);
+
+    /* anisotropic filtering */
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_ANISOTROPY_EXT, 8);
+
+    /* how OpenGL combines the colors from texels with the color of the underlying
+     * geometry is controlled by the texture environment mode */
+    glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
+
+    /* once texture is loaded and enabled, it will applied to every primitive
+     * that specifies coordinates, ORLY? */
+    glEnable(GL_TEXTURE_2D);
+
+    /* specular highlights for textured items */
+    glLightModeli(GL_LIGHT_MODEL_COLOR_CONTROL, GL_SEPARATE_SPECULAR_COLOR);
+
+    /* gray background */
+    glClearColor(0.5f, 0.5f, 0.5f, 1.0f);
+}
+
+static void keys(SDL_keysym *keysym, unsigned int *keys_held)
+{
+    switch (keysym->sym)
+    {
+        case SDLK_ESCAPE:
+            program_running = 0;
+            break;
+        default:
+            break;
+    }
+}
+
+/* process SDL events */
+static void process_events(void)
+{
+    SDL_Event event;
+    unsigned static int keys_held[323];
+    SDLKey sym;
+
+    while (SDL_PollEvent(&event))
+    {
+        sym = event.key.keysym.sym;
+
+        switch (event.type)
+        {
+            case SDL_KEYUP:
+            {
+                /* reset the key to 0 */
+                keys_held[sym] = 0;
+                break;
+            }
+            case SDL_KEYDOWN:
+            {
+                keys_held[sym] = 1;
+                keys(&event.key.keysym, keys_held);
+                break;
+            }
+            case SDL_VIDEORESIZE:
+            {
+                resize(event.resize.w, event.resize.h);
+                break;
+            }
+            case SDL_QUIT:
+            {
+                program_running = 0;
+                break;
+            }
+            default:
+                break;
+        }
+    }
+}
+
+static void setup_sdl(void)
+{
+    if (SDL_Init(SDL_INIT_VIDEO) < 0 )
+    {
+        fprintf(stderr, "SDL: unable to init, %s\n", SDL_GetError());
+        exit(-1);
+    }
+    atexit(SDL_Quit);
+    SDL_WM_SetCaption("Programmable Pipeline", NULL);
+
+    SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 8);
+    SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 8);
+    SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 8);
+    SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE, 8);
+    SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
+    SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
+
+    if ((screen = SDL_SetVideoMode(320, 240, 32, SDL_OPENGL | SDL_RESIZABLE)) == NULL)
+    {
+        fprintf(stderr, "SDL: unable to set video mode: %s\n", SDL_GetError());
+        exit(-1);
+    }
+
+    SDL_EnableUNICODE(1);
+    /* SDL doesn't trigger off a ResizeEvent at startup, but as we need this
+     * for OpenGL, we do this ourselves */
+    SDL_Event resizeEvent;
+    resizeEvent.type = SDL_VIDEORESIZE;
+    resizeEvent.resize.w = 320;
+    resizeEvent.resize.h = 240;
+    SDL_PushEvent(&resizeEvent);
+}
+
+static void setup_glew(void)
+{
+    /* initalize glew */
+    GLenum glewerr = glewInit();
+    if (GLEW_OK != glewerr)
+    {
+        fprintf(stderr, "GLEW error: %s\n", glewGetErrorString(glewerr));
+        exit(-1);
+    }
+    else
+        fprintf(stdout, "GLEW: using version %s\n", glewGetString(GLEW_VERSION));
+
+    /* display OpenGL version */
+    GLint major;
+    GLint minor;
+    glGetIntegerv(GL_MAJOR_VERSION, &major);
+    glGetIntegerv(GL_MINOR_VERSION, &minor);
+    fprintf(stdout, "GLEW: initialized OpenGL %d.%d\n", major, minor);
+}
+
+static int fragprog_create(GLuint *handle, const char *frag_src)
+{
+    if (!handle)
+        return -1;
+
+    GLint ret, length;
+    GLuint fragment;
+
+    /* create handle */
+    fragment = glCreateShader(GL_FRAGMENT_SHADER);
+
+    /* specify shader text */
+    glShaderSource(fragment, 1, &frag_src, NULL);
+
+    /* compile shader and check for any errors */
+    glCompileShader(fragment);
+    glGetShaderiv(fragment, GL_COMPILE_STATUS, &ret);
+    if (!ret)
+    {
+        glGetShaderiv(fragment, GL_INFO_LOG_LENGTH, &length);
+        GLchar info_log[length];
+        glGetShaderInfoLog(fragment, length, NULL, info_log);
+        fprintf(stderr, "%s", info_log);
+        glDeleteShader(fragment);
+        return -1;
+    }
+
+    /* save the handle */
+    *handle = fragment;
+
+    return 0;
+}
+
+static int vertprog_create(GLuint *handle, const char *vert_src)
+{
+    if (!handle)
+        return -1;
+
+    GLint ret, length;
+    GLuint vertex;
+
+    /* create handle */
+    vertex = glCreateShader(GL_VERTEX_SHADER);
+
+    /* specify shader text */
+    glShaderSource(vertex, 1, &vert_src, NULL);
+
+    /* compile shader and check for any errors */
+    glCompileShader(vertex);
+    glGetShaderiv(vertex, GL_COMPILE_STATUS, &ret);
+    if (!ret)
+    {
+        glGetShaderiv(vertex, GL_INFO_LOG_LENGTH, &length);
+        GLchar info_log[length];
+        glGetShaderInfoLog(vertex, length, NULL, info_log);
+        fprintf(stderr, "%s", info_log);
+        glDeleteShader(vertex);
+        return -1;
+    }
+
+    /* save the handle */
+    *handle = vertex;
+
+    return 0;
+}
+
+static int prog_create(GLuint *prog_handle, GLuint *vert_handle, GLuint *frag_handle)
+{
+    if (!prog_handle || !vert_handle || !frag_handle)
+        return -1;
+
+    GLint ret, length;
+    GLuint program;
+
+    /* create handle */
+    program = glCreateProgram();
+
+    /* attach shaders */
+    glAttachShader(program, *vert_handle);
+    glAttachShader(program, *frag_handle);
+
+    /* link, should be done whenever we attach or detach shaders to program */
+    glLinkProgram(program);
+    glGetProgramiv(program, GL_LINK_STATUS, &ret);
+    if (!ret)
+    {
+        glGetProgramiv(program, GL_INFO_LOG_LENGTH, &length);
+        GLchar info_log[length];
+        glGetProgramInfoLog(program, length, NULL, info_log);
+        fprintf(stderr, "%s", info_log);
+        glDeleteProgram(program);
+        return -1;
+    }
+
+    /* validate the program, should be done whenever program is linked or relinked */
+    glValidateProgram(program);
+    glGetProgramiv(program, GL_VALIDATE_STATUS, &ret);
+    if (!ret)
+    {
+        glGetProgramiv(program, GL_INFO_LOG_LENGTH, &length);
+        GLchar info_log[length];
+        glGetProgramInfoLog(program, length, NULL, info_log);
+        fprintf(stderr, "%s", info_log);
+        glDeleteProgram(program);
+        return -1;
+    }
+
+    /* save the handle */
+    *prog_handle = program;
+
+    return 0;
+}
+
+static void render(void)
+{
+    /* clear the window with current clearing color */
+    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
+
+    /* save the matrix state */
+    glPushMatrix();
+    {
+        /* draw ground using immiediate mode */
+        glDisable(GL_MULTISAMPLE);
+        glEnable(GL_BLEND);
+        glEnable(GL_LINE_SMOOTH);
+
+        GLfloat fExtent = 20.0f;
+        GLfloat fStep = 0.5f;
+        GLfloat y = -0.4f;
+        GLfloat iLine;
+
+        glLineWidth(1.0f);
+        glBegin(GL_LINES);
+        for (iLine = -fExtent; iLine <= fExtent; iLine += fStep)
+        {
+            glVertex3f(iLine, y, fExtent);
+            glVertex3f(iLine, y, -fExtent);
+            glVertex3f(fExtent, y, iLine);
+            glVertex3f(-fExtent, y, iLine);
+        }
+        glEnd();
+
+        glDisable(GL_LINE_SMOOTH);
+        glDisable(GL_BLEND);
+        glEnable(GL_MULTISAMPLE);
+        /* end of ground */
+
+        glPushMatrix();
+            /* draw vbo */
+            glTranslatef(0.0f, 0.0f, -4.0f);
+            gltDrawVBOInterleaved(buffer_objects, 3, GL_TRIANGLES);
+        glPopMatrix();
+    }
+    /* restore the matrix state */
+    glPopMatrix();
+
+    /* buffer swap */
+    SDL_GL_SwapBuffers();
+}
+
+static void setup_vbo(void)
+{
+    /* setup a vbo triangle */
+    float vert_arr[9] = {
+    0.0f, 0.0f,  0.0f,
+    1.0f, 0.0f,  0.0f,
+    0.5f, 0.83f, 0.0f };
+
+    float norm_arr[9] = {
+    0.0f, 0.0f, 1.0f,
+    0.0f, 0.0f, 1.0f,
+    0.0f, 0.0f, 1.0f };
+
+    float texcoord_arr[6] = {
+    0.0f, 0.0f,
+    1.0f, 0.0f,
+    0.5f, 1.0f };
+
+    unsigned char color_arr[9] = {
+    255, 0, 0,
+    0, 255, 0,
+    0, 0, 255 };
+
+    unsigned short indices_arr[3] = { 0, 1, 2 };
+
+    gltGenVBOInterleaved(buffer_objects, vert_arr, texcoord_arr, norm_arr,
+                         color_arr, indices_arr, 3, 3);
+    gl_error_check(__FUNCTION__, __FILE__, __LINE__);
+}
+
+static void setup_shaders(void)
+{
+#if 0
+    char *vert_src, *frag_src;
+    loadfile_to_mem("vert", &vert_src);
+    loadfile_to_mem("frag", &frag_src);
+    free(vert_src);
+    free(frag_src);
+#endif
+
+    vertprog_create(&p.vert, vshader);
+    fragprog_create(&p.frag, fshader);
+    prog_create(&p.prog, &p.vert, &p.frag);
+
+    /* this is where the magic happens, fixed-functionality is replaced depending
+     * on what shaders are attached to the program */
+    glUseProgram(p.prog);
+
+    /* find out where the flicker constant lives, program has to be in use */
+    GLint flickerLocation = glGetUniformLocation(p.prog, "flickerFactor");
+    /* initially set the blink parameter to 1 (no flicker) */
+    if (flickerLocation != -1)
+        glUniform1f(flickerLocation, 1.0f);
+}
+
+static void dump_shaders(void)
+{
+    FILE *f1, *f2;
+    f1 = fopen("vert", "w");
+    f2 = fopen("frag", "w");
+
+    if (f1 && f2)
+    {
+        fwrite(vshader, sizeof(char), sizeof(vshader), f1);
+        fwrite(fshader, sizeof(char), sizeof(fshader), f2);
+
+        fclose(f1);
+        fclose(f2);
+    }
+    else
+        fprintf(stderr, "%s: failed\n", __FUNCTION__);
+}
+
+int main(int argc, char **argv)
+{
+    setup_sdl();
+    setup_glew();
+    setup_opengl();
+    /* would also check for vert and frag extensions, otherwise use fixed-func */
+    setup_vbo();
+    setup_shaders();
+    gl_error_check(__FUNCTION__, __FILE__, __LINE__);
+
+    /* main loop */
+    while (program_running)
+    {
+        process_events();
+        render();
+    }
+    gl_error_check(__FUNCTION__, __FILE__, __LINE__);
+
+    /* cleanup */
+    glDeleteProgram(p.prog); /* automatically detaches any shaders */
+    glDeleteShader(p.vert);
+    glDeleteShader(p.frag);
+    glDeleteBuffers(3, buffer_objects);
+    if (screen)
+        SDL_FreeSurface(screen);
+
+    puts("bye!");
+
+    return 0;
+}
+