I'm trying to make an app that draws an image in Android Studio with NDK and JNI to call C++ Code using OpenGL ES. I have went through the tutorial how to do this in OpenGL at : https://learnopengl.com/#!Getting-started/Textures, which use GLSL 330 core. However, OpenGL ES 3.0 isn't supported on the Android emulator (Note in this link :https://developer.android.com/ndk/guides/stable_apis.html).
Therefore, I have to use the GLSL ES #version 100 , which doesn't support "layout", "in" and "out" in the shaders below. How should I edit them so that they could run in #version 100 and is there any change in the source code if I edit them? Thanks for your attention and your help.
Update: After searching around, I found out that I could use glGetAttributeLocation to get the location of variable in vertex shader instead of using layout(location=0). However, there's no VAO in GLSL ES #version 100 so I still couldn't firgure out how it work without VAO.
My Vertex shader:
#version 330 core
layout (location = 0) in vec3 position;
layout (location = 1) in vec3 color;
layout (location = 2) in vec2 texCoord;
out vec3 ourColor;
out vec2 TexCoord;
void main()
{
gl_Position = vec4(position, 1.0f);
ourColor = color;
// We swap the y-axis by substracing our coordinates from 1. This is done because most images have the top y-axis inversed with OpenGL's top y-axis.
// TexCoord = texCoord;
TexCoord = vec2(texCoord.x, 1.0 - texCoord.y);
}
fragment Shader:
#version 330 core
in vec3 ourColor;
in vec2 TexCoord;
out vec4 color;
// Texture samplers
uniform sampler2D ourTexture1;
uniform sampler2D ourTexture2;
void main()
{
// Linearly interpolate between both textures (second texture is only slightly combined)
color = mix(texture(ourTexture1, TexCoord), texture(ourTexture2, TexCoord), 0.2);
}
Initialize VAO,VBO,:
// Set up vertex data (and buffer(s)) and attribute pointers
GLfloat vertices[] = {
// Positions // Colors // Texture Coords
0.5f, 0.5f, 0.0f, 1.0f, 0.0f, 0.0f, 1.0f, 1.0f, // Top Right
0.5f, -0.5f, 0.0f, 0.0f, 1.0f, 0.0f, 1.0f, 0.0f, // Bottom Right
-0.5f, -0.5f, 0.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f, // Bottom Left
-0.5f, 0.5f, 0.0f, 1.0f, 1.0f, 0.0f, 0.0f, 1.0f // Top Left
};
GLuint indices[] = { // Note that we start from 0!
0, 1, 3, // First Triangle
1, 2, 3 // Second Triangle
};
GLuint VBO, VAO, ;
glGenVertexArrays(1, &VAO);
glGenBuffers(1, &VBO);
glGenBuffers(1, &);
glBindVertexArray(VAO);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, );
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);
// Position attribute
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)0);
glEnableVertexAttribArray(0);
// Color attribute
glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)(3 * sizeof(GLfloat)));
glEnableVertexAttribArray(1);
// TexCoord attribute
glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)(6 * sizeof(GLfloat)));
glEnableVertexAttribArray(2);
glBindVertexArray(0); // Unbind VAO
Draw an image:
// Clear the colorbuffer
glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
// Activate shader
ourShader.Use();
// Bind Textures using texture units
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, texture1);
glUniform1i(glGetUniformLocation(ourShader.Program, "ourTexture1"), 0);
glActiveTexture(GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D, texture2);
glUniform1i(glGetUniformLocation(ourShader.Program, "ourTexture2"), 1);
// Draw container
glBindVertexArray(VAO);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
glBindVertexArray(0);
Finally, I manage to solve it. In GLSL ES 100, There is no in out and layout(location=0) as i mentioned above. Therefore, I have to replace them:
in => attribute
out => varying
And completely remove layout(location=0) because there's no such thing does the same thing in GLSL ES 100 as far as I aware.
Because of the removal of layout(location=0), we have to tell the program the location of our vertex data, which are position,color and textCoord in this case. With layout(location=0), we could simple put the location 0 in the
glVertexAttribPointer(0,3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)0);
glEnableVertexAttribArray(0);
Without it, we first need to get the location of the vertex attribute with:
GLint mPosition= glGetAttributeLocation(ourProgram,"position")
then replace the constant number 0,1 or 2 with my predefined mPosition :
glVertexAttribPointer(mPosition,3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)0);
glEnableVertexAttribArray(mPosition);;
The same on color and textCoord.
below are my edited vertex shader, fragment shader and how to initialize VBO and pass in our data:
Edited vertex shader for GLSL ES 100:
auto gVertexShader =
"attribute vec3 position;\n"
"attribute vec3 color;\n"
"attribute vec2 texCoord;\n"
"varying vec3 ourColor;\n"
"varying vec2 TexCoord;\n"
"void main()\n"
"{\n"
"gl_Position = vec4(position,1.0); // Add the xOffset to the x position of the vertex position\n"
"ourColor = color;\n"
"TexCoord= vec2(texCoord.x,1.0-texCoord.y);\n"
"}\n";
Edited fragment shader for GLSL ES 100:
static const char FRAGMENT_SHADER[] =
"#version 100\n"
"precision mediump float;\n"
"varying vec4 vColor;\n"
"void main() {\n"
" gl_FragColor = vColor;\n"
"}\n";
my InitBuffer function:
// Set up vertex data (and buffer(s)) and attribute pointers
GLfloat vertices[] = {
// Positions // Colors // Texture Coords
0.5f, 0.5f, 0.0f, 1.0f, 0.0f, 0.0f, 1.0f, 1.0f, // Top Right
0.5f, -0.5f, 0.0f, 0.0f, 1.0f, 0.0f, 1.0f, 0.0f, // Bottom Right
-0.5f, -0.5f, 0.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f, // Bottom Left
-0.5f, 0.5f, 0.0f, 1.0f, 1.0f, 0.0f, 0.0f, 1.0f // Top Left
};
GLuint indices[] = { // Note that we start from 0!
0, 1, 3, // First Triangle
1, 2, 3 // Second Triangle
};
void initBuffers()
{
GLint mPosition,mCorlor,mTextCoord;
GLuint VBOs[2]; // Initialize an buffer to store all the verticles and transfer them to the GPU
glGenBuffers(2, VBOs); // Generate VBO
glBindBuffer(GL_ARRAY_BUFFER, VBOs[0]);//Bind verticles array for OpenGL to use
glBufferData(GL_ARRAY_BUFFER, sizeof(recVertices), recVertices, GL_STATIC_DRAW);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, VBOs[1]);//Bind the indices for information about drawing sequence
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);
// 1. set the vertex attributes pointers
// Position Attribute
mPosition=glGetAttributeLocation(Program, "position");
glVertexAttribPointer(mPosition, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)0);
glEnableVertexAttribArray(mPosition);
// Color Attribute
mColor=glGetAttributeLocation(Program, "color");
glVertexAttribPointer(mColor, 3, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)(3 * sizeof(GLfloat)));
glEnableVertexAttribArray(mColor);
//Texture Coordinate Attribute
mTextCoord=glGetAttributeLocation(Program, "textCoord")'
glVertexAttribPointer(mTextCoord, 2, GL_FLOAT, GL_FALSE, 8 * sizeof(GLfloat), (GLvoid*)(6 * sizeof(GLfloat)));
glEnableVertexAttribArray(mTextCoord);
}
Then we replace VAO binding in our draw function with the call of initBuffer() function
// Clear the colorbuffer
glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
// Activate shader
ourShader.Use();
// Bind Textures using texture units
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, texture1);
glUniform1i(glGetUniformLocation(ourShader.Program, "ourTexture1"), 0);
glActiveTexture(GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D, texture2);
glUniform1i(glGetUniformLocation(ourShader.Program, "ourTexture2"), 1);
// Draw container
initBuffers();
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
glBindVertexArray(0);
Hope this will help who has the same problem with me. Please feel free to ask me if you have any question :).