SDL_GL_BindTexture
Use this function to bind an OpenGL/ES/ES2 texture to the current context for use with OpenGL instructions when rendering OpenGL primitives directly.
Contents
Syntax
int SDL_GL_BindTexture(SDL_Texture* texture,
float* texw,
float* texh)
Function Parameters
texture |
the texture to bind to the current OpenGL/ES/ES2 context |
texw |
a pointer to a float value which will be filled with the texture width or NULL if you don't need that value |
texh |
a pointer to a float value which will be filled with the texture height or NULL if you don't need that value |
Return Value
Returns 0 on success, or -1 if the operation is not supported; call SDL_GetError() for more information.
Code Examples
The following are three examples extracted from the Ignifuga Game Engine that show how to integrate libRocket (which uses OpenGL for rendering) with SDL2.
void RocketSDLRenderInterfaceOpenGL::RenderGeometry(Rocket::Core::Vertex* vertices, int num_vertices, int* indices, int num_indices, const Rocket::Core::TextureHandle texture, const Rocket::Core::Vector2f& translation)
{
// SDL uses shaders that we need to disable here
render_data.glUseProgramObjectARB(0);
render_data.glPushMatrix();
render_data.glTranslatef(translation.x, translation.y, 0);
std::vector<Rocket::Core::Vector2f> Positions(num_vertices);
std::vector<Rocket::Core::Colourb> Colors(num_vertices);
std::vector<Rocket::Core::Vector2f> TexCoords(num_vertices);
float texw, texh;
SDL_Texture* sdl_texture = NULL;
if(texture) {
render_data.glEnableClientState(GL_TEXTURE_COORD_ARRAY);
sdl_texture = (SDL_Texture *) texture;
SDL_GL_BindTexture(sdl_texture, &texw, &texh);
}
for (int i = 0; i < num_vertices; i++) {
Positions[i] = vertices[i].position;
Colors[i] = vertices[i].colour;
if (sdl_texture) {
TexCoords[i].x = vertices[i].tex_coord.x * texw;
TexCoords[i].y = vertices[i].tex_coord.y * texh;
} else {
TexCoords[i] = vertices[i].tex_coord;
}
}
render_data.glEnableClientState(GL_VERTEX_ARRAY);
render_data.glEnableClientState(GL_COLOR_ARRAY);
render_data.glVertexPointer(2, GL_FLOAT, 0, &Positions[0]);
render_data.glColorPointer(4, GL_UNSIGNED_BYTE, 0, &Colors[0]);
render_data.glTexCoordPointer(2, GL_FLOAT, 0, &TexCoords[0]);
render_data.glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
render_data.glEnable(GL_BLEND);
render_data.glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
render_data.glDrawElements(GL_TRIANGLES, num_indices, GL_UNSIGNED_INT, indices);
render_data.glDisableClientState(GL_VERTEX_ARRAY);
render_data.glDisableClientState(GL_COLOR_ARRAY);
if (sdl_texture) {
SDL_GL_UnbindTexture(sdl_texture);
render_data.glDisableClientState(GL_TEXTURE_COORD_ARRAY);
}
render_data.glColor4f(1.0, 1.0, 1.0, 1.0);
render_data.glPopMatrix();
}
void RocketSDLRenderInterfaceOpenGLES::RenderGeometry(Rocket::Core::Vertex* vertices, int num_vertices, int* indices, int num_indices, const Rocket::Core::TextureHandle texture, const Rocket::Core::Vector2f& translation)
{
render_data.glPushMatrix();
render_data.glTranslatef(translation.x, translation.y, 0);
std::vector<Rocket::Core::Vector2f> Positions(num_vertices);
std::vector<Rocket::Core::Colourb> Colors(num_vertices);
std::vector<Rocket::Core::Vector2f> TexCoords(num_vertices);
float texw, texh;
SDL_Texture* sdl_texture = NULL;
if(texture) {
render_data.glEnableClientState(GL_TEXTURE_COORD_ARRAY);
sdl_texture = (SDL_Texture *) texture;
SDL_GL_BindTexture(sdl_texture, &texw, &texh);
}
for (int i = 0; i < num_vertices; i++) {
Positions[i] = vertices[i].position;
Colors[i] = vertices[i].colour;
if (sdl_texture) {
TexCoords[i].x = vertices[i].tex_coord.x * texw;
TexCoords[i].y = vertices[i].tex_coord.y * texh;
} else {
TexCoords[i] = vertices[i].tex_coord;
}
}
unsigned short newIndicies[num_indices];
for (int i = 0; i < num_indices; i++) {
newIndicies[i] = (unsigned short) indices[i];
}
render_data.glEnableClientState(GL_VERTEX_ARRAY);
render_data.glEnableClientState(GL_COLOR_ARRAY);
render_data.glVertexPointer(2, GL_FLOAT, 0, &Positions[0]);
render_data.glColorPointer(4, GL_UNSIGNED_BYTE, 0, &Colors[0]);
render_data.glTexCoordPointer(2, GL_FLOAT, 0, &TexCoords[0]);
render_data.glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
render_data.glEnable(GL_BLEND);
render_data.glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
render_data.glDrawElements(GL_TRIANGLES, num_indices, GL_UNSIGNED_SHORT, newIndicies);
render_data.glDisableClientState(GL_VERTEX_ARRAY);
render_data.glDisableClientState(GL_COLOR_ARRAY);
render_data.glDisableClientState(GL_TEXTURE_COORD_ARRAY);
if (sdl_texture) {
SDL_GL_UnbindTexture(sdl_texture);
render_data.glDisableClientState(GL_TEXTURE_COORD_ARRAY);
}
render_data.glColor4f(1.0, 1.0, 1.0, 1.0);
render_data.glPopMatrix();
}
SDL_Texture* sdl_texture = NULL;
if(texture) render_data.glUseProgram(program_texture_id);
else render_data.glUseProgram(program_color_id);
int width, height;
SDL_Rect rvp;
SDL_RenderGetViewport(renderer, &rvp);
GLfloat projection[4][4];
// Prepare an orthographic projection
projection[0][0] = 2.0f / rvp.w;
projection[0][1] = 0.0f;
projection[0][2] = 0.0f;
projection[0][3] = 0.0f;
projection[1][0] = 0.0f;
//if (renderer->target) {
// projection[1][1] = 2.0f / height;
//} else {
projection[1][1] = -2.0f / rvp.h;
//}
projection[1][2] = 0.0f;
projection[1][3] = 0.0f;
projection[2][0] = 0.0f;
projection[2][1] = 0.0f;
projection[2][2] = 0.0f;
projection[2][3] = 0.0f;
projection[3][0] = -1.0f;
//if (renderer->target) {
// projection[3][1] = -1.0f;
//} else {
projection[3][1] = 1.0f;
//}
projection[3][2] = 0.0f;
projection[3][3] = 1.0f;
// Set the projection matrix
if (texture) {
render_data.glUniformMatrix4fv(u_texture_projection, 1, GL_FALSE, (GLfloat *)projection);
render_data.glUniform2f(u_texture_translation, translation.x, translation.y);
} else {
render_data.glUniformMatrix4fv(u_color_projection, 1, GL_FALSE, (GLfloat *)projection);
render_data.glUniform2f(u_color_translation, translation.x, translation.y);
}
render_data.glEnable(GL_BLEND);
render_data.glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
float texw, texh;
unsigned short newIndicies[num_indices];
for (int i = 0; i < num_indices; i++) {
newIndicies[i] = (unsigned short) indices[i];
}
glVertexAttribPointer(ROCKETGLUE_ATTRIBUTE_POSITION, 2, GL_FLOAT, GL_FALSE, sizeof(Rocket::Core::Vertex), &vertices[0].position);
glVertexAttribPointer(ROCKETGLUE_ATTRIBUTE_COLOR, 4, GL_UNSIGNED_BYTE, GL_TRUE, sizeof(Rocket::Core::Vertex), &vertices[0].colour);
render_data.glEnableVertexAttribArray(ROCKETGLUE_ATTRIBUTE_POSITION);
render_data.glEnableVertexAttribArray(ROCKETGLUE_ATTRIBUTE_TEXCOORD);
render_data.glEnableVertexAttribArray(ROCKETGLUE_ATTRIBUTE_COLOR);
if (texture) {
sdl_texture = (SDL_Texture *) texture;
SDL_GL_BindTexture(sdl_texture, &texw, &texh);
render_data.glUniform1i(u_texture, 0);
glVertexAttribPointer(ROCKETGLUE_ATTRIBUTE_TEXCOORD, 2, GL_FLOAT, GL_FALSE, sizeof(Rocket::Core::Vertex), &vertices[0].tex_coord);
} else {
render_data.glActiveTexture(GL_TEXTURE0);
render_data.glDisable(GL_TEXTURE_2D);
render_data.glDisableVertexAttribArray(ROCKETGLUE_ATTRIBUTE_TEXCOORD);
}
render_data.glDrawElements(GL_TRIANGLES, num_indices, GL_UNSIGNED_SHORT, newIndicies);
/* We can disable ROCKETGLUE_ATTRIBUTE_COLOR (2) safely as SDL will reenable the vertex attrib 2 if it is required */
render_data.glDisableVertexAttribArray(ROCKETGLUE_ATTRIBUTE_COLOR);
/* Leave ROCKETGLUE_ATTRIBUTE_POSITION (0) and ROCKETGLUE_ATTRIBUTE_TEXCOORD (1) enabled for compatibility with SDL which
doesn't re enable them when you call RenderCopy/Ex */
if(sdl_texture) SDL_GL_UnbindTexture(sdl_texture);
else render_data.glEnableVertexAttribArray(ROCKETGLUE_ATTRIBUTE_TEXCOORD);
/* Reset blending and draw a fake point just outside the screen to let SDL know that it needs to reset its state in case it wants to render a texture */
render_data.glDisable(GL_BLEND);
SDL_SetRenderDrawBlendMode(renderer, SDL_BLENDMODE_NONE);
SDL_RenderDrawPoint(renderer, -1, -1);
Remarks
If provided, texw and texh will be filled with the width and height values suitable for the provided texture. In most cases, both will be 1.0, however, on systems that support the GL_ARB_texture_rectangle extension, these values will actually be the pixel width and height used to create the texture, so this factor needs to be taken into account when providing texture coordinates to OpenGL.
You need a renderer to create a SDL_Texture, therefore you can only use this function with an implicit OpenGL context from SDL_CreateRenderer(), not with your own OpenGL context. If you need control over your OpenGL context, you need to write your own texture-loading methods.
Also note that SDL may upload RGB textures as BGR (or vice-versa), and re-order the color channels in the shaders phase, so the uploaded texture may have swapped color channels.
Version
This function is available since SDL 2.0.0.
