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icecubeflower

OpenGL SDL_image to textured quad

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Hey I've a got 2D game going on. I used SDL and also OpenGL. For loading images I always use .TGA's and I load them myself with code I mostly took from NeHe's site. It's like this: I declare this data type:
struct TextureImage
{
   GLubyte *imageData;
   GLuint bpp;
   GLuint width;
   GLuint height;
   GLuint texID;
};

Then I declare some variable:
TextureImage *whatever;

Then I declare this function:
bool LoadTGA(TextureImage *texture, string &filename)
{
   GLubyte TGAheader[12]={0,0,2,0,0,0,0,0,0,0,0,0};
   GLubyte TGAcompare[12];
   GLubyte header[6];
   GLuint bytesPerPixel;
   GLuint imageSize;
   GLuint temp;
   GLuint type=GL_RGBA;

   FILE *file = fopen(filename.c_str(), "rb");

   if(file==NULL||
      fread(TGAcompare,1,sizeof(TGAcompare),file)!=sizeof(TGAcompare)||
      memcmp(TGAheader,TGAcompare,sizeof(TGAheader))!=0||
      fread(header,1,sizeof(header),file)!=sizeof(header))
   {
      if(file!=NULL)
         fclose(file);
      return false;
   }
   texture->width  = header[1] * 256 + header[0];
   texture->height = header[3] * 256 + header[2];

   if(texture->width<=0||texture->height<=0||(header[4]!=24 && header[4]!=32))
   {
      fclose(file);
      return false;
   }

   texture->bpp=header[4];
   bytesPerPixel=texture->bpp/8;
   imageSize=texture->width*texture->height*bytesPerPixel;

   texture->imageData = (GLubyte *)malloc(imageSize);  //Ah, malloc, C's answer to "new".  So when is this memory freed?
                                                       //you have to free it yourself NeHe has a Deinitialize function

   if(texture->imageData==NULL||fread(texture->imageData, 1, imageSize, file)!=imageSize)
   {
      if(texture->imageData!=NULL)
      {
         free(texture->imageData);  //well, I guess this is how you free it
         texture->imageData = NULL;
      }
      fclose(file);
      return false;
   }

   //for a fun time comment this out
   for(GLuint i=0; i<(unsigned int)imageSize; i+=bytesPerPixel)
   {
      temp=texture->imageData;
      texture->imageData = texture->imageData[i + 2];
      texture->imageData[i + 2] = temp;
   }

   fclose (file);

   // Build A Texture From The Data
   glGenTextures(1, &texture[0].texID);  //texture is a pointer to a TextureImage
                                         //why not just texture.texID?  why &texture[0]??  wtf
                                         //the the address of a pointer?  the first element of it?  it has no elements, wtf?
                                         //wtf could [0] possibly mean?
   //oh I remember, you use -> for pointers instead of . like above
   //so here he wants to use . so maybe ampersand on a pointer "converts" it back to a regular data type?
   //I have no idea what's going on

   glBindTexture(GL_TEXTURE_2D, texture[0].texID);  //And here it needs no ampersand.  Why?  I don't know.
   glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
   glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

   if(texture[0].bpp==24)
   {
      type=GL_RGB;
   }

   //Here using . instead of -> so maybe [0] takes care of it?  Then why the ampersand above?
   glTexImage2D(GL_TEXTURE_2D, 0, type, texture[0].width, texture[0].height,0, type, GL_UNSIGNED_BYTE, texture[0].imageData);

   return true;
}

So now I pass *whatever to that function along with the name of a .tga file and I can bind *whatever whenver I want and slap on some quads.
glBindTexture(GL_TEXTURE_2D, whatever.texID);
glBegin(GL_POLYGON);
   glTexCoord2f(0.0,1.0);	glVertex3f(0,768,0.0);
   glTexCoord2f(1.0,1.0);	glVertex3f(1024,768,0.0);
   glTexCoord2f(1.0,0.0);	glVertex3f(1024,0,0.0);
   glTexCoord2f(0.0,0.0);	glVertex3f(0,0,0.0);
glEnd();

But TGA's always take up a few trillion terrabytes and no one's used them since Fred Flintstone so I want to start loading .PNG's instead. I want to use SDL_image loader and using SDL_image loader for an SDL game is easy enough except I want it to load the PNG into a data type that I can bind to an OpenGL texture like I'm doing above with .tga's. I cannot find how to do this. I don't think it would take more than a page of code, I figured there would be something out there I could just block copy and figure out later but I can't find anything. I don't know why, lots of people have probably loaded .png's with SDL_image and textured OpenGL quads with them.

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Enjoy all the love of many different formats the SDL_IMage loads


bool TextureLoader::Load(std::string& filename)
{
SDL_Surface* tex = IMG_Load(filename.c_str());
if(!tex)
return false;
//setup your texture parameters however you like here
glBindTexture(...);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB8, tex->w, tex->h, 0, GL_RGB, GL_UNSIGNED_BYTE, tex->pixels);

SDL_FreeSurface(tex);
return true;
}





[Edited by - MARS_999 on July 9, 2008 1:30:19 AM]

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I don't really get it. What is this TextureLoader class? Am I supposed to write it myself and add imageWidth and all those variables to it and add the Load(string) function?

It looks to me like all it does is return true. tex is freed at the end, I don't see what the result is. I need something that I can bind and then map to a quad. Sorry I'm probably just not understanding it, I don't understand graphics very well.

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Quote:
Original post by icecubeflower
I don't really get it. What is this TextureLoader class? Am I supposed to write it myself and add imageWidth and all those variables to it and add the Load(string) function?

It looks to me like all it does is return true. tex is freed at the end, I don't see what the result is. I need something that I can bind and then map to a quad. Sorry I'm probably just not understanding it, I don't understand graphics very well.


When you call glTexImage2d, it will actually copy the data over to the video card, not just bind it. Once you done this it isn't necessary to keep the image loaded. In his snippet, he only shows how to use SDL's image library capabilities. You can use your knowledge on OpenGL's texture ability with his code to -texture a quad-. He also didn't show exactly how the params are passes as it isn't necessary, you can come up with it.

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Why do I need to make a TextureLoader class? Why do I need a class? Why can't I just make a function like this:


void Load(SDL_Surface* tex, std::string& filename)
{
tex = IMG_Load(filename.c_str());
if(!tex)
return false;
//setup your texture parameters however you like here

return true;
}



And then after I use that function I have my tex variable to work with so I can go like this back in my main program:


glBindTexture(...);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB8, tex->w, tex->h, 0, GL_RGB, GL_UNSIGNED_BYTE, tex->pixels);
SDL_FreeSurface(tex);



Really I'm not even sure why I even need that glTexImage2D function. Usually I just bind a texture and then draw a quad and I'm done. Unless I need glTexImage2D back in my Load function?

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The function you are questioning is what dumps the image into video memory! This way the video card can use its own memory rather than the slow transfer of ram -> video ram.

Here is a snippet of my texture class:

#include "Texture.h"
#include <string>
#include <sdl/sdl_image.h>
#include <sdl/sdl_opengl.h>

Texture::Texture(const char *filename)
{
// Load Texture into Memory
SDL_Surface *image = IMG_Load(filename);
if(!image)
throw std::pair<const char*, const char*>("Texture::Texture", "Error Loading Image from Disk");

// Create Video-Card Texture
glGenTextures(1, &tex_id);
glBindTexture(GL_TEXTURE_2D, tex_id);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, image->w, image->h, 0, GL_RGBA, GL_UNSIGNED_BYTE, image->pixels);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

SDL_FreeSurface(image);
}


void Texture::Bind()
{
glBindTexture(GL_TEXTURE_2D, tex_id);
}



Using something like this makes it a little neater (at least in my opinion) when binding different textures at different instances. Also the destructor can take care of any texture releasing, etc, if needed to be done in real time. =)

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I think I almost get it. That *image you declared is used and then freed on the spot. Before it's freed the image is loaded into video memory via that function I dared to question. So that function call goes out of scope. Now anytime I draw a quad that texture is going to be mapped to it until I call Texture::Texture(const char *filename) again. Am I right?

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For small projects, keep all of the texture objects in video memory. Bind which ever texture you need to use by calling the Bind method in the class, that way the next textured raster being rendered it will use the newly bound texture without having to do any IO (still in video memory). Basically the less IO you do, the faster... Much faster. :)

One way I have been doing this is creating a texture manager, where it will load images from a directory, than the user can request a reference of the texture object for rendering. Once the manager goes out of scope all the resources are freed.

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Sorry man, I don't really understand what you just said.

I don't really understand how the textures you have loaded into video memory are ever accessed again. When I did it with the LoadTGA(TextureImage *texture, string &filename) function that I listed in my first post *texture was NOT freed at the end like your *image is. It's up to me to make sure it's freed later.

That way whenever I load a new map and new monsters I assign a TextureImage* to every new TGA file by sending it into my LoadTGA() function along with the name of the file. Then my Draw() function executes continuously but as it draws the map and hero and monsters it just binds those TextureImage*'s over and over.

Your *image is freed at the end of the function. It is bound so it can be texture mapped right then. But then if something else is bound then it seems to me that the image is lost.

I just don't see how you can free the image from memory right after you bind it. The Draw() function uses that image every cycle. Why would you free it?

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      // [the following code includes all used gl* functions, other parts are due to readability partialy excluded] // glfw: initialize and configure // ------------------------------ glfwInit(); glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4); glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 4); glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE); // glfw window creation // -------------------- GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL); if (window == NULL) { cout << "Failed to create GLFW window" << endl; glfwTerminate(); return -1; } glfwMakeContextCurrent(window); glfwSetFramebufferSizeCallback(window, framebuffer_size_callback); glfwSetCursorPosCallback(window, mouse_callback); glfwSetScrollCallback(window, scroll_callback); // tell GLFW to capture our mouse glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED); // glad: load all OpenGL function pointers // --------------------------------------- if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)) { cout << "Failed to initialize GLAD" << endl; return -1; } // ==================================================================================================== // window and functions are set up // ==================================================================================================== // configure global opengl state // ----------------------------- glEnable(GL_DEPTH_TEST); glEnable(GL_CULL_FACE); // build and compile our shader program [...] // set up vertex data (and buffer(s)) and configure vertex attributes [...] // shader configuration [...] // render loop // =========== while (!glfwWindowShouldClose(window)) { // input processing and fps calculation[...] // render // ------ glClearColor(0.1f, 0.1f, 0.1f, 1.0f); glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glDepthMask(GL_TRUE); //enable depth writing glDepthFunc(GL_LEQUAL); //avoid z-fighting //draw ambient component into color and depth buffer view = camera.GetViewMatrix(); projection = glm::perspective(glm::radians(camera.Zoom), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 100.0f); // setting up lighting shader for ambient pass [...] // render the cubes glBindVertexArray(cubeVAO); for (unsigned int i = 0; i < 10; i++) { //position cube [...] glDrawArrays(GL_TRIANGLES, 0, 36); } //------------------------------------------------------------------------------------------------------------------------ glDepthMask(GL_FALSE); //disable depth writing glEnable(GL_BLEND); glBlendFunc(GL_ONE, GL_ONE); //additive blending glEnable(GL_STENCIL_TEST); //setting up shadowShader and lightingShader [...] for (int light = 0; light < lightsused; light++) { glDepthFunc(GL_LESS); glClear(GL_STENCIL_BUFFER_BIT); //configure stencil ops for front- and backface to write according to z-fail glStencilOpSeparate(GL_FRONT, GL_KEEP, GL_DECR_WRAP, GL_KEEP); //-1 for front-facing glStencilOpSeparate(GL_BACK, GL_KEEP, GL_INCR_WRAP, GL_KEEP); //+1 for back-facing glStencilFunc(GL_ALWAYS, 0, GL_TRUE); //stencil test always passes if(hidevolumes) glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE); //disable writing to the color buffer glDisable(GL_CULL_FACE); glEnable(GL_DEPTH_CLAMP); //necessary to render SVs into infinity //draw SV------------------- shadowShader.use(); shadowShader.setInt("lightnr", light); int nr; if (onecaster) nr = 1; else nr = 10; for (int i = 0; i < nr; i++) { //position cube[...] glDrawArrays(GL_TRIANGLES, 0, 36); } //-------------------------- glDisable(GL_DEPTH_CLAMP); glEnable(GL_CULL_FACE); glStencilFunc(GL_EQUAL, 0, GL_TRUE); //stencil test passes for ==0 so only for non shadowed areas glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP); //keep stencil values for illumination glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE); //enable writing to the color buffer glDepthFunc(GL_LEQUAL); //avoid z-fighting //draw diffuse and specular pass lightingShader.use(); lightingShader.setInt("lightnr", light); // render the cubes for (unsigned int i = 0; i < 10; i++) { //position cube[...] glDrawArrays(GL_TRIANGLES, 0, 36); } } glDisable(GL_BLEND); glDepthMask(GL_TRUE); //enable depth writing glDisable(GL_STENCIL_TEST); //------------------------------------------------------------------------------------------------------------------------ // also draw the lamp object(s) [...] // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.) // ------------------------------------------------------------------------------- glfwSwapBuffers(window); glfwP } // optional: de-allocate all resources once they've outlived their purpose: // ------------------------------------------------------------------------ glDeleteVertexArrays(1, &cubeVAO); glDeleteVertexArrays(1, &lightVAO); glDeleteBuffers(1, &VBO); // glfw: terminate, clearing all previously allocated GLFW resources. // ------------------------------------------------------------------ glfwTerminate(); return 0;  
    • By Green_Baron
      Hi,
      i am self teaching me graphics and oo programming and came upon this:
      My Window class creates an input handler instance, the glfw user pointer is redirected to that object and methods there do the input handling for keyboard and mouse. That works. Now as part of the input handling i have an orbiting camera that is controlled by mouse movement. GLFW_CURSOR_DISABLED is set as proposed in the glfw manual. The manual says that in this case the cursor is automagically reset to the window's center. But if i don't reset it manually with glfwSetCursorPos( center ) mouse values seem to add up until the scene is locked up.
      Here are some code snippets, mostly standard from tutorials:
      // EventHandler m_eventHandler = new EventHandler( this, glm::vec3( 0.0f, 5.0f, 0.0f ), glm::vec3( 0.0f, 1.0f, 0.0f ) ); glfwSetWindowUserPointer( m_window, m_eventHandler ); m_eventHandler->setCallbacks(); Creation of the input handler during window creation. For now, the camera is part of the input handler, hence the two vectors (position, up-vector).  In future i'll take that functionally out into an own class that inherits from the event handler.
      void EventHandler::setCallbacks() { glfwSetCursorPosCallback( m_window->getWindow(), cursorPosCallback ); glfwSetKeyCallback( m_window->getWindow(), keyCallback ); glfwSetScrollCallback( m_window->getWindow(), scrollCallback ); glfwSetMouseButtonCallback( m_window->getWindow(), mouseButtonCallback ); } Set callbacks in the input handler.
      // static void EventHandler::cursorPosCallback( GLFWwindow *w, double x, double y ) { EventHandler *c = reinterpret_cast<EventHandler *>( glfwGetWindowUserPointer( w ) ); c->onMouseMove( (float)x, (float)y ); } Example for the cursor pos callback redirection to a class method.
      // virtual void EventHandler::onMouseMove( float x, float y ) { if( x != 0 || y != 0 ) { // @todo cursor should be set automatically, according to doc if( m_window->isCursorDisabled() ) glfwSetCursorPos( m_window->getWindow(), m_center.x, m_center.y ); // switch up/down because its more intuitive m_yaw += m_mouseSensitivity * ( m_center.x - x ); m_pitch += m_mouseSensitivity * ( m_center.y - y ); // to avoid locking if( m_pitch > 89.0f ) m_pitch = 89.0f; if( m_pitch < -89.0f ) m_pitch = -89.0f; // Update Front, Right and Up Vectors updateCameraVectors(); } } // onMouseMove() Mouse movement processor method. The interesting part is the manual reset of the mouse position that made the thing work ...
      // straight line distance between the camera and look at point, here (0,0,0) float distance = glm::length( m_target - m_position ); // Calculate the camera position using the distance and angles float camX = distance * -std::sin( glm::radians( m_yaw ) ) * std::cos( glm::radians( m_pitch) ); float camY = distance * -std::sin( glm::radians( m_pitch) ); float camZ = -distance * std::cos( glm::radians( m_yaw ) ) * std::cos( glm::radians( m_pitch) ); // Set the camera position and perspective vectors m_position = glm::vec3( camX, camY, camZ ); m_front = glm::vec3( 0.0, 0.0, 0.0 ) - m_position; m_up = m_worldUp; m_right = glm::normalize( glm::cross( m_front, m_worldUp ) ); glm::lookAt( m_position, m_front, m_up ); Orbiting camera vectors calculation in updateCameraVectors().
      Now, for my understanding, as the glfw manual explicitly states that if cursor is disabled then it is reset to the center, but my code only works if it is reset manually, i fear i am doing something wrong. It is not world moving (only if there is a world to render :-)), but somehow i am curious what i am missing.
       
      I am not a professional programmer, just a hobbyist, so it may well be that i got something principally wrong :-)
      And thanks for any hints and so ...
       
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