path: root/sdl/gltools.c

/* gltools.c
 *
 * OpenGL Tools
 *
 *
 */

#include <GL/glew.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "gltools.h"

/* mipmapping enabled by default */
GLuint gltLoadTGATexture(const char *fname)
{
    GLuint handle;

    /* variables used for texture loading */
    GLbyte *pBytes;
    GLint iWidth, iHeight, iComponents;
    GLenum eFormat;

    glGenTextures(1, &handle);
    glBindTexture(GL_TEXTURE_2D, handle);

    /* load texture */
    glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP, GL_TRUE);
    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

    pBytes = gltLoadTGA(fname, &iWidth, &iHeight, &iComponents, &eFormat);
    if (!pBytes)
    {
        fprintf(stderr, "gltLoadTGA: failed to load texture!\n");
        return -1;
    }

    glTexImage2D(GL_TEXTURE_2D, 0, iComponents, iWidth, iHeight, 0, eFormat,
                 GL_UNSIGNED_BYTE, pBytes);
    free(pBytes);

    /* seems like mipmapping only applies to MIN_FILTER since mipmapping divides
     * current texture into smaller and smaller pieces
     */
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR); /* GL_LINEAR to disable mipmapping */
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

    return handle;
}

void gltListExtensions(void)
{
    const GLubyte *ext_str;
    char *ext_str_copy;

    ext_str = glGetString(GL_EXTENSIONS);
    if (!ext_str)
        return;

    ext_str_copy = (char *) malloc(strlen((char *) ext_str) + 1);
    if (!ext_str_copy)
    {
        fprintf(stderr, "gltListExtensions failed, %s:%d\n", __FILE__, __LINE__);
        perror("malloc");
        exit(-1);
    }

    strcpy(ext_str_copy, (char *) ext_str);

    char *tok;
    while ((tok = strsep(&ext_str_copy, " ")))
        printf("%s\n", tok);

    if (ext_str_copy)
        free(ext_str_copy);
}

void gltOpenGLInfo(void)
{
    const GLubyte *str;

    str = glGetString(GL_VENDOR);
    fprintf(stdout, "OpenGL vendor: %s\n", str ? (char *) str : "unknown");
    str = glGetString(GL_RENDERER);
    fprintf(stdout, "OpenGL renderer: %s\n", str ? (char *) str : "unknown");
    str = glGetString(GL_VERSION);
    fprintf(stdout, "OpenGL version: %s\n", str ? (char *) str : "unknown");
    str = glGetString(GL_SHADING_LANGUAGE_VERSION);
    fprintf(stdout, "GLSL version: %s\n", str ? (char *) str : "unknown");
}

GLboolean gltQueryExtension(const char *extName)
{
    char *p = (char *) glGetString(GL_EXTENSIONS);
    char *end = p + strlen(p);

    while (p < end)
    {
        int n = strcspn(p, " ");

        if ((strlen(extName) == n) && (strncmp(extName, p, n) == 0))
            return GL_TRUE;

        p += (n + 1);
    }

    return GL_FALSE;
}

GLint gltWriteTGA(const char *szFileName)
{
    FILE *pFile;              /* file pointer */
    TGAHEADER tgaHeader;      /* tga file header */
    unsigned long lImageSize; /* size in bytes of image */
    GLbyte *pBits = NULL;     /* pointer to bits */
    GLint iViewport[4];       /* viewport in pixels */
    GLenum lastBuffer;        /* storage for the current read buffer setting */

    /* get the viewport dimensions */
    glGetIntegerv(GL_VIEWPORT, iViewport);

    /* how big is the image going to be (targas are tightly packed) */
    lImageSize = iViewport[2] * 3 * iViewport[3];

    /* allocate block, if this doesn't work, go home */
    pBits = (GLbyte *) malloc(lImageSize);
    if (pBits == NULL)
    {
        perror("malloc");
        return 0;
    }

    /* change how bits are stored */
    glPixelStorei(GL_PACK_ALIGNMENT, 1);
    glPixelStorei(GL_PACK_ROW_LENGTH, 0);
    glPixelStorei(GL_PACK_SKIP_ROWS, 0);
    glPixelStorei(GL_PACK_SKIP_PIXELS, 0);

    /* get the current read buffer setting and save it, switch to
     * the front buffer and do the read operation, finally, restore
     * the read buffer state
     */
    glGetIntegerv(GL_READ_BUFFER, (GLint *) &lastBuffer);
    glReadBuffer(GL_FRONT);
    glReadPixels(0, 0, iViewport[2], iViewport[3], GL_BGR_EXT,
    GL_UNSIGNED_BYTE, pBits);
    glReadBuffer(lastBuffer);

    /* initialize the targa header */
    tgaHeader.identsize = 0;
    tgaHeader.colorMapType = 0;
    tgaHeader.imageType = 2;
    tgaHeader.colorMapStart = 0;
    tgaHeader.colorMapLength = 0;
    tgaHeader.colorMapBits = 0;
    tgaHeader.xstart = 0;
    tgaHeader.ystart = 0;
    tgaHeader.width = iViewport[2];
    tgaHeader.height = iViewport[3];
    tgaHeader.bits = 24;
    tgaHeader.descriptor = 0;

    /* attempt to open the file */
    pFile = fopen(szFileName, "wb");
    if (pFile == NULL)
    {
        perror("fopen");
        free(pBits); /* free buffer and return error */
        return 0;
    }

    /* write the header */
    fwrite(&tgaHeader, sizeof(TGAHEADER), 1, pFile);

    /* write the image data */
    fwrite(pBits, lImageSize, 1, pFile);

    /* free temporary buffer and close the file */
    free(pBits);
    fclose(pFile);

    return 1;
}

GLbyte *gltLoadTGA(const char *szFileName, GLint *iWidth, GLint *iHeight,
                   GLint *iComponents, GLenum *eFormat)
{
    FILE *pFile;              /* file pointer */
    TGAHEADER tgaHeader;      /* TGA file header */
    unsigned long lImageSize; /* size in bytes of image */
    short sDepth;             /* pixel depth; */
    GLbyte *pBits = NULL;     /* pointer to bits */

    /* default/failed values */
    *iWidth = 0;
    *iHeight = 0;
    *eFormat = GL_BGR_EXT;
    *iComponents = GL_RGB8;

    /* attempt to open the file */
    pFile = fopen(szFileName, "rb");
    if (pFile == NULL)
    {
        perror("fopen");
        return 0;
    }

    /* read in header (binary) */
    fread(&tgaHeader, 18 /* sizeof(TGAHEADER) */, 1, pFile);

    /* get width, height, and depth of texture */
    *iWidth = tgaHeader.width;
    *iHeight = tgaHeader.height;
    sDepth = tgaHeader.bits / 8;

    /* put some validity checks here, very simply, i only understand
     * or care about 8, 24, or 32 bit targas
     */
    if (tgaHeader.bits != 8 && tgaHeader.bits != 24 && tgaHeader.bits != 32)
        return NULL;

    /* calculate size of image buffer */
    lImageSize = tgaHeader.width * tgaHeader.height * sDepth;

    /* allocate memory and check for success */
    pBits = (GLbyte *) malloc(lImageSize * sizeof(GLbyte));
    if (pBits == NULL)
    {
        perror("malloc");
        return NULL;
    }

    /* read in the bits */
    /* check for read error, this should catch rle or other  */
    /* weird formats that i don't want to recognize */
    if (fread(pBits, lImageSize, 1, pFile) != 1)
    {
        perror("fread");
        free(pBits);
        return NULL;
    }

    /* set opengl format expected */
    switch (sDepth)
    {
        case 3: /* most likely case */
            *eFormat = GL_BGR_EXT;
            *iComponents = GL_RGB8;
            break;
        case 4:
            *eFormat = GL_BGRA_EXT;
            *iComponents = GL_RGBA8;
            break;
        case 1:
            *eFormat = GL_LUMINANCE;
            *iComponents = GL_LUMINANCE8;
            break;
    }

    /* done with file */
    fclose(pFile);

    /* return pointer to image data */
    return pBits;
}

#ifdef _WIN32
/* this function is insane in a good way */
char *strsep(char **stringp, const char *delim)
{
    char *result;

    if ((stringp == NULL) || (*stringp == NULL))
        return NULL;

    result = *stringp;

    while (**stringp && !strchr(delim, **stringp))
        ++*stringp;

    if (**stringp)
        *(*stringp)++ = '\0';
    else
        *stringp = NULL;

    return result;
}
#endif