Load multi texture opengl es 2.0 - c++

Question

i'm found this piece of code on internet about how to load multi texture in opengl es 2.0:
//
// Book: OpenGL(R) ES 2.0 Programming Guide
// Authors: Aaftab Munshi, Dan Ginsburg, Dave Shreiner
// ISBN-10: 0321502795
// ISBN-13: 9780321502797
// Publisher: Addison-Wesley Professional
// URLs: http://safari.informit.com/9780321563835
// http://www.opengles-book.com
//
// MultiTexture.c
//
// This is an example that draws a quad with a basemap and
// lightmap to demonstrate multitexturing.
//
#include"pch.h"
#include <stdlib.h>
typedef struct
{
// Handle to a program object
GLuint programObject;
// Attribute locations
GLint positionLoc;
GLint texCoordLoc;
// Sampler locations
GLint baseMapLoc;
GLint lightMapLoc;
// Texture handle
GLuint baseMapTexId;
GLuint lightMapTexId;
} UserData;
///
// Load texture from disk
//
GLuint LoadTexture(char *fileName)
{
int width,
height;
char *buffer = esLoadTGA(fileName, &width, &height);
GLuint texId;
if (buffer == NULL)
{
esLogMessage("Error loading (%s) image.\n", fileName);
return 0;
}
glGenTextures(1, &texId);
glBindTexture(GL_TEXTURE_2D, texId);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, buffer);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
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);
free(buffer);
return texId;
}
///
// Initialize the shader and program object
//
int Init(ESContext *esContext)
{
UserData *userData = (UserData*) esContext->userData;
const char vShaderStr[] =
"attribute vec4 a_position; \n"
"attribute vec2 a_texCoord; \n"
"varying vec2 v_texCoord; \n"
"void main() \n"
"{ \n"
" gl_Position = a_position; \n"
" v_texCoord = a_texCoord; \n"
"} \n";
const char fShaderStr[] =
"precision mediump float; \n"
"varying vec2 v_texCoord; \n"
"uniform sampler2D s_baseMap; \n"
"uniform sampler2D s_lightMap; \n"
"void main() \n"
"{ \n"
" vec4 baseColor; \n"
" vec4 lightColor; \n"
" \n"
" baseColor = texture2D( s_baseMap, v_texCoord ); \n"
" lightColor = texture2D( s_lightMap, v_texCoord ); \n"
" gl_FragColor = baseColor * (lightColor + 0.25); \n"
"} \n";
// Load the shaders and get a linked program object
userData->programObject = esLoadProgram(vShaderStr, fShaderStr);
// Get the attribute locations
userData->positionLoc = glGetAttribLocation(userData->programObject, "a_position");
userData->texCoordLoc = glGetAttribLocation(userData->programObject, "a_texCoord");
// Get the sampler location
userData->baseMapLoc = glGetUniformLocation(userData->programObject, "s_baseMap");
userData->lightMapLoc = glGetUniformLocation(userData->programObject, "s_lightMap");
// Load the textures
userData->baseMapTexId = LoadTexture("basemap.tga");
userData->lightMapTexId = LoadTexture("lightmap.tga");
if (userData->baseMapTexId == 0 || userData->lightMapTexId == 0)
return FALSE;
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
return TRUE;
}
///
// Draw a triangle using the shader pair created in Init()
//
void Draw(ESContext *esContext)
{
UserData *userData = (UserData*)esContext->userData;
GLfloat vVertices[] = { -0.5f, 0.5f, 0.0f, // Position 0
0.0f, 0.0f, // TexCoord 0
-0.5f, -0.5f, 0.0f, // Position 1
0.0f, 1.0f, // TexCoord 1
0.5f, -0.5f, 0.0f, // Position 2
1.0f, 1.0f, // TexCoord 2
0.5f, 0.5f, 0.0f, // Position 3
1.0f, 0.0f // TexCoord 3
};
GLushort indices[] = { 0, 1, 2, 0, 2, 3 };
// Set the viewport
glViewport(0, 0, esContext->width, esContext->height);
// Clear the color buffer
glClear(GL_COLOR_BUFFER_BIT);
// Use the program object
glUseProgram(userData->programObject);
// Load the vertex position
glVertexAttribPointer(userData->positionLoc, 3, GL_FLOAT,
GL_FALSE, 5 * sizeof(GLfloat), vVertices);
// Load the texture coordinate
glVertexAttribPointer(userData->texCoordLoc, 2, GL_FLOAT,
GL_FALSE, 5 * sizeof(GLfloat), &vVertices[3]);
glEnableVertexAttribArray(userData->positionLoc);
glEnableVertexAttribArray(userData->texCoordLoc);
// Bind the base map
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, userData->baseMapTexId);
// Set the base map sampler to texture unit to 0
glUniform1i(userData->baseMapLoc, 0);
// Bind the light map
glActiveTexture(GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D, userData->lightMapTexId);
// Set the light map sampler to texture unit 1
glUniform1i(userData->lightMapLoc, 1);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_SHORT, indices);
eglSwapBuffers(esContext->eglDisplay, esContext->eglSurface);
}
///
// Cleanup
//
void ShutDown(ESContext *esContext)
{
UserData *userData = (UserData*)esContext->userData;
// Delete texture object
glDeleteTextures(1, &userData->baseMapTexId);
glDeleteTextures(1, &userData->lightMapTexId);
// Delete program object
glDeleteProgram(userData->programObject);
}
int main(int argc, char *argv[])
{
ESContext esContext;
UserData userData;
esInitContext(&esContext);
esContext.userData = &userData;
esCreateWindow(&esContext, L"MultiTexture", 320, 240, ES_WINDOW_RGB);
if (!Init(&esContext))
return 0;
esRegisterDrawFunc(&esContext, Draw);
esMainLoop(&esContext);
ShutDown(&esContext);
}
but when i run this it shows only dark! debugging the code shows that nothing is null or anything,so what's wrong with it?
i add two files named same as in the code but still i see a dark space!
any suggestion?
and another question is this is the common way to load any number of texture i want or not?

Answer 1

Try to draw a red square first (use gl_FragColor = vec4(1.0,0.0,0.0,1.0) ). If nothing draws, then change the order of your indices (you might have the normal backwards).
2nd , you need to commit the texture to the GPU before drawing.
You release the buffer before the GPU gets the chance of taking over the memory (you call free(buffer) before drawing anything with that texture, the buffer isn't on the GPU memory yet).
To commit a texture, draw something with that texture.
Here's a sample code of force commit (feel free to adapt it to your needs) :
void cColorTest::ForceCommitTexture(unsigned int texId)
{
glUseProgram(m_nProgram);
glBindTexture(GL_TEXTURE_2D,texId);
GLfloat triangle[]= { 0.0f, 0.5f, 0.5f, 1.0f, 1.0f, 0.0f,
-0.5f, -0.5f, 0.5f, 1.0f, 0.0f, 1.0f,
0.5f, -0.5f, 0.5f, 1.0f, 0.0f, 0.0f};
glVertexAttribPointer ( m_nPosLoc, 4, GL_FLOAT, GL_FALSE, 6 * sizeof(float), triangle );
glEnableVertexAttribArray ( m_nPosLoc );
glVertexAttribPointer ( m_nUVLoc, 2, GL_FLOAT, GL_FALSE, 6 * sizeof(float), triangle + 4 );
glEnableVertexAttribArray ( m_nUVLoc );
glDrawArrays(GL_TRIANGLES,0,1);
}