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gmanouvrier
11-26-2013, 01:54 PM
Hi,

As a beginer i try to load a png texture(with tranparancy)
After having read some docs and forum i succeeded in loading png (without transparancy) as a texture into a 2D quad.
Fact is i encounter some troubles with transparancy.
I saw some important rules to apply : glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA) for exemple and gl_enabled(GL_BLEND).
I still have a badly formated picture.

Maybe i do something wrong, maybe instructions are not in the good order.

This is my code, maybe somone could see where the issue come from?




int main(int argc, char *argv[]){
SDL_Event event;
SDL_Init(SDL_INIT_VIDEO);
SDL_SetVideoMode(1200, 700, 0, SDL_OPENGL | SDL_HWSURFACE | SDL_NOFRAME);

glViewport(0, 0, 1200, 700);
// glClearColor(0.0, 0.0, 0.0, 1.0);
//glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_PROJECTION);
glMatrixMode(GL_MODELVIEW);
//glEnable(GL_DEPTH_TEST);

int width(191);
int height(240);

texture = LoadTexture_png("pmario.png",width,height);
SDL_EnableKeyRepeat(10,10);
while(SDL_WaitEvent(&event))
{
switch(event.type)
{
case SDL_QUIT:
exit(0);
break;
case SDL_KEYDOWN:
switch (event.key.keysym.sym)
{
case SDLK_ESCAPE:
exit(0);
break;
}
}



glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode( GL_MODELVIEW );
glLoadIdentity( );
glEnable(GL_BLEND);
glDisable(GL_DEPTH_TEST);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);


glEnable(GL_TEXTURE_2D);

glBegin(GL_QUADS);
glBindTexture(GL_TEXTURE_2D, texture);
glTexCoord2d(0,1);glVertex2f(-0.8, 0.8);

glTexCoord2d(1,1); glVertex2f(-0.6, 0.8);
glTexCoord2d(1,0);glVertex2f(-0.6, 0.4);
glTexCoord2d(0,0); glVertex2f(-0.8, 0.4);
glEnd();
glDisable(GL_TEXTURE_2D);
glDisable(GL_BLEND);

SDL_GL_SwapBuffers();


}







For instance i use a loading png function i found on the web :




GLuint LoadTexture_png(const char* filename, int &width, int &height)
{
//header for testing if it is a png
png_byte header[8];

//open file as binary
FILE *fp = fopen(filename, "rb");
if (!fp) {
return TEXTURE_LOAD_ERROR;
}

//read the header
fread(header, 1, 8, fp);

//test if png
int is_png = !png_sig_cmp(header, 0, 8);
if (!is_png) {
fclose(fp);
return TEXTURE_LOAD_ERROR;
}

//create png struct
png_structp png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL,
NULL, NULL);
if (!png_ptr) {
fclose(fp);
return (TEXTURE_LOAD_ERROR);
}

//create png info struct
png_infop info_ptr = png_create_info_struct(png_ptr);
if (!info_ptr) {
png_destroy_read_struct(&png_ptr, (png_infopp) NULL, (png_infopp) NULL);
fclose(fp);
return (TEXTURE_LOAD_ERROR);
}

//create png info struct
png_infop end_info = png_create_info_struct(png_ptr);
if (!end_info) {
png_destroy_read_struct(&png_ptr, &info_ptr, (png_infopp) NULL);
fclose(fp);
return (TEXTURE_LOAD_ERROR);
}

//png error stuff, not sure libpng man suggests this.
if (setjmp(png_jmpbuf(png_ptr))) {
png_destroy_read_struct(&png_ptr, &info_ptr, &end_info);
fclose(fp);
return (TEXTURE_LOAD_ERROR);
}

//init png reading
png_init_io(png_ptr, fp);

//let libpng know you already read the first 8 bytes
png_set_sig_bytes(png_ptr, 8);

// read all the info up to the image data
png_read_info(png_ptr, info_ptr);

//variables to pass to get info
int bit_depth, color_type;
png_uint_32 twidth, theight;

// get info about png
png_get_IHDR(png_ptr, info_ptr, &twidth, &theight, &bit_depth, &color_type,
NULL, NULL, NULL);

//update width and height based on png info
width = twidth;
height = theight;

// Update the png info struct.
png_read_update_info(png_ptr, info_ptr);

// Row size in bytes.
int rowbytes = png_get_rowbytes(png_ptr, info_ptr);

// Allocate the image_data as a big block, to be given to opengl
png_byte *image_data = new png_byte[rowbytes * height];
if (!image_data) {
//clean up memory and close stuff
png_destroy_read_struct(&png_ptr, &info_ptr, &end_info);
fclose(fp);
return TEXTURE_LOAD_ERROR;
}

//row_pointers is for pointing to image_data for reading the png with libpng
png_bytep *row_pointers = new png_bytep[height];
if (!row_pointers) {
//clean up memory and close stuff
png_destroy_read_struct(&png_ptr, &info_ptr, &end_info);
delete[] image_data;
fclose(fp);
return TEXTURE_LOAD_ERROR;
}
// set the individual row_pointers to point at the correct offsets of image_data
for (int i = 0; i < height; ++i)
row_pointers[height - 1 - i] = image_data + i * rowbytes;

//read the png into image_data through row_pointers
png_read_image(png_ptr, row_pointers);

//Now generate the OpenGL texture object
GLuint texture;
glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);
glTexImage2D(GL_TEXTURE_2D,0, GL_RGBA, width, height, 0,
GL_RGB, GL_UNSIGNED_BYTE, (GLvoid*) image_data);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

//clean up memory and close stuff
png_destroy_read_struct(&png_ptr, &info_ptr, &end_info);
delete[] image_data;
delete[] row_pointers;
fclose(fp);

return texture;
}





The png i use :

RGBA (i checked it, it is a png with alpha for transparancy)
color depth 32
size 191 X 240
Thanks a lot for your help,

Gilles

tonyo_au
11-27-2013, 05:27 PM
I still have a badly formated picture.
Can you be more specific

gmanouvrier
11-28-2013, 01:31 AM
Hi,

Fact is i was using an old opengl Version. I assume with opengl3 or more, it will be ok.
Image was unreadable(visually). I have difficulties to fond the english word ;) it sounds like picture was badly rendered (like a tv with bad setting ;) ).

Thanks,

Gilles

tonyo_au
11-28-2013, 02:16 PM
glTexImage2D(GL_TEXTURE_2D,0, GL_RGBA, width, height, 0,
GL_RGB, GL_UNSIGNED_BYTE, (GLvoid*) image_data);


You have to check it the image is RGB or RGBA. This state says that the image is RGB which is unlikely if you have an alpha value.